Caramelized Onion and Portobello Mushroom Sliders with Fry Sauce

Vegetarian Sliders with Fry Sauce — Meatless comfort food at its finest! The filling features a caramelized Vidalia onion, baby portobello mushrooms, and pickles.

Best Veggie Sliders Recipe 

These vegetarian sliders are filling, satisfying, meatless, and definitely healthier than a greasy burger or typical cookout fare. Try them for a meatless weeknight dinner if you’re trying to lighten things up.

For the filling, I caramelized a Vidalia onion in olive oil along with baby portobello mushrooms and pickles. The resulting combo is a meaty (minus the meat) sandwich that’s hearty, chewy, with subtle crunch from the onions and pickles.

I used Bread and Butter Chips from Farmer’s Garden® by Vlasic®. I love pickles, but many brands are loaded with a ridiculous amount of sodium, which is why I’ve started pickling my own vegetables. 

Thankfully the Vlasic pickles aren’t salt bombs and I love their sweet-and-tangy zip. They’re artisanal-quality, premium pickles, made with honest ingredients and no artificial flavors. They’re made with deliciously ripe cucumbers, whole garlic cloves, slices of red bell pepper, rounds of carrots, fresh herbs and spices, and hand-packed in glass jars.

Before filling the sliders, I coated the bread with fry sauce. If you’ve never had it, you’ve got to try it. Sometimes fry sauce is called Utah sauce or Utah fry sauce, but I waitressed in a dive bar in Minnesota in college and this is the sauce we served with wings and waffle fries so it’s not just a Utah thing.

It’s two parts ketchup to 1 part mayo (use vegan mayo) with a splash of pickle juice. Now you have a use for pickle juice rather than just tossing it.

The sauce is excellent on fries, but it makes a great sandwich spread and even for mayo-haters, it’s not overly mayo-ey.  I like a little food with my bowl of sauce or dip and can devour a batch on about 7 fries.

I loved this filling mixture and didn’t even need buns. My family didn’t even realize it was meatless. Comfort food at its finest.

Ingredients for Vegetarian Sliders

To make these onion and mushroom sliders, you’ll need: 

• Sweet Vidalia onion
• Olive oil
• Baby portobello mushrooms 
• Bread and butter pickles
• Pickle juice
• Slider buns or Hawaiian rolls
• Ketchup 
• Mayonnaise or Miracle Whip
• Onion powder

How to Make Vegetarian Sliders

These easy vegetarian sliders come together quickly and require minimal assembly. Here’s how the filling is prepared and the sliders are assembled: 

1. Make the filling: Caramelize the onionsin a non-stick skillet over medium-high heat.  It takes about 10 minutes for my onions to caramelize and I cook them covered to save time. 
2. Once the onion has caramelized, add the mushrooms, pickles, pickle juice, a little more oil, and allow mixture to cook for about 10 minutes, stirring every couple of minutes.
3. Make the fry sauce: In a medium bowl, combine all ingredients and whisk until smooth.
4. Assemble the sliders: Generously spread fry sauce on both sides of slider buns.
5. Fill each bun generously with the onion mixture and serve. 

Can This Recipe Be Made in Advance? 

If you plan on making these vegetarian sliders for a party, you can make the filling up to 3 days in advance and the fry sauce up to 1 week in advance. When you’re ready to serve, simply reheat the filling in a skillet and then assemble the sliders as instructed. 

What to Serve with Veggie Sliders

To make the portobello sliders a meal, serve them with one or more of the following sides: 

• Grilled Mexican Corn 
• Crispy Parmesan Ranch Potatoes
• Grilled Vegetables
• Tropical Fruit Salad
• Broccoli Salad
• Homemade Seasoned Fries

Tips for the Best Vegetarian Sliders

Have patience when cooking the mushrooms and onions. The filling takes about 20 minutes total to cook — do not crank up the heat to save time as that will result in a less rich filling. 

However, you can always pop the lid on your skillet to safely speed up the cook time. That’s what I did! 

Leftover fry sauce is delicious slathered on wraps and sandwiches, and can also be used as a dipping sauce. 

Save Saved Review Print

5 from 1 vote

Vegetarian Sliders with Fry Sauce

By Averie Sunshine

Meatless comfort food at its finest! The filling features a caramelized Vidalia onion, baby portobello mushrooms, and pickles.

Prep Time: 10 minutes minutes

Cook Time: 20 minutes minutes

Total Time: 30 minutes minutes

Servings: 6

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Ingredients 

Sliders

• ▢ 1 medium sweet Vidalia onion or yellow onion, peeled and sliced
• ▢ 2 to 3 tablespoons olive oil, divided
• ▢ 4 ounces sliced baby portobello mushrooms
• ▢ 1 cup diced Vlasic Farmer’s Garden Bread and Butter Chip pickles
• ▢ 1 teaspoon pickle juice
• ▢ 6 slider buns, or Hawaiian rolls

Fry Sauce

• ▢ ½ cup ketchup
• ▢ ¼ cup mayo, or Miracle Whip, use vegan mayo to keep vegan
• ▢ about 3 teaspoons pickle juice, or to taste
• ▢ pinch onion powder, optional and to taste

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Instructions 

Filling:

• Heat a non-stick skillet over medium-high heat, add the onion, drizzle with about 1 tablespoon oil, and allow onion to caramelize, stirring every couple of minutes, or as needed. It takes about 10 minutes for my onions to caramelize and I cook them covered to save time. Lower the heat if onion is browning too fast.
• After onion has caramelized, add the mushrooms, pickles, pickle juice, 1 to 2 tablespoons oil or as necessary, and allow mixture  to cook for about 10 minutes, stirring every couple of minutes, or as needed. I cook covered to save time. After about 10 minutes, or after vegetables have softened and wilted, turn off the heat; set aside.
• While vegetables are cooking, make the fry sauce.

Fry Sauce:

• In a medium bowl, combine all ingredients and whisk until smooth.
• Generously spread fry sauce on both sides of slider buns.
• Fill each bun generously with the onion mixture and serve.

Notes

Storage: Sliders are best warm and fresh although extra filling will keep airtight in the fridge for up to 3 days. Extra fry sauce will keep airtight in the fridge for up to 1 month.

Nutrition

Serving: 1, Calories: 541kcal, Carbohydrates: 30g, Protein: 6g, Fat: 46g, Saturated Fat: 22g, Polyunsaturated Fat: 21g, Trans Fat: 1g, Cholesterol: 85mg, Sodium: 797mg, Fiber: 3g, Sugar: 11g

Nutrition information is automatically calculated, so should only be used as an approximation.

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