Spinach Stuffed Portobellos

These delicious stuffed portobello mushrooms make a great low carb vegan or vegetarian main dish or side dish. The combination of spinach, Parmesan, and mozzarella creates a rich and flavorful filling that pairs perfectly with the meaty texture of the portobello mushrooms.

Ingredients for Spinach Stuffed Portobello Mushrooms

You will need the following:

4 large portobello mushrooms
1 tablespoon olive oil
1 tablespoon balsamic vinegar
1/2 teaspoon garlic powder
10 ounce package frozen spinach, thawed and squeezed thoroughly to remove excess water
1/2 cup Parmesan cheese, grated
1 cup mozzarella cheese, shredded
1/2 teaspoon salt
1/2 teaspoon ground black pepper
red pepper flakes, optional for serving

Ingredient Notes

Portobello Mushrooms: Removing the gills from the inside of the mushrooms creates more space for the filling and helps reduce moisture during cooking.
Olive Oil: Extra virgin olive oil adds a rich flavor.
Balsamic Vinegar: Regular balsamic adds depth and a hint of sweetness.
Garlic Powder: Adds a subtle, savory kick to the mushrooms.
Frozen Spinach: To avoid a watery filling, squeeze out all excess water after thawing. Fresh baby spinach can also be used; simply cook it in a skillet until wilted, set aside to cook, and then squeeze out the excess liquid.
Parmesan Cheese: Adds a sharp, nutty flavor to the filling. I used Violife brand vegan Parmesan cheese.
Mozzarella Cheese: Provides a gooey, melty texture that complements the other ingredients.
Salt and Ground Black Pepper: Essential for seasoning to taste; use about 1/2 teaspoon of each to enhance the overall flavor.

How to Make Spinach Stuffed Portobello Mushrooms

STEP ONE: Preheat the oven to 450°F. Line a rimmed roasting sheet pan with aluminum foil for easy cleanup.

STEP TWO: Prepare the Mushrooms. Remove and discard the mushroom stems. Wipe away any dirt with a damp paper towel. Scrape the stem side of the mushrooms with a spoon to remove the gills.

STEP THREE: Coat the Mushrooms. In a small bowl, whisk together the olive oil, balsamic vinegar, and garlic powder. Brush the mixture on the outside and inside of the portobello caps.

STEP FOUR: Roast the Mushrooms. Place the coated mushroom caps stem-side down on the prepared sheet pan. Roast for 5 minutes. Remove the mushroom caps and discard any excess liquid that has been released during roasting. Place the caps back onto the sheet pan, stem-side up. Lower the oven temperature to 400°F.

STEP FIVE: Prepare the Filling. In a medium bowl, combine the spinach, Parmesan cheese, mozzarella cheese, salt, and black pepper. Adjust seasoning to taste. Generously fill each of the mushrooms with the spinach mixture.

STEP SIX: Finish Cooking. Return the stuffed mushrooms to the oven for 5 minutes, just enough to warm and soften the cheese. Sprinkle with red pepper flakes, if using, and serve immediately.

Tips for Success with Stuffed Mushrooms

Remove Gills: Removing the gills from portobello mushrooms makes more room for the filling and reduces excess moisture.
Stem Side Down: Mushrooms can hold a lot of water. Place the mushrooms stem side down for the first roasting to release excess water.
Thawing Spinach: Thaw frozen spinach thoroughly and squeeze out excess water to avoid a soggy filling.
Roasting Pan: Use a heavy-duty roasting pan as high temperatures can warp a standard baking sheet.

FAQ

How do I best thaw and squeeze water from frozen spinach? Thaw the spinach in the refrigerator or microwave. Once thawed, place it in a clean kitchen towel and squeeze out as much water as possible to avoid a watery filling.
Do I have to remove the gills? No, but you should for this recipe. Removing the gills is recommended because it creates more space for the filling. Leaving the gills of a portobello mushroom in can result in a dish that’s too dark and earthy in flavor.
Can I use different types of cheese? Yes, feel free to experiment with other cheeses, such as feta, goat cheese, or even cheddar, for a different flavor profile.
Can I add other vegetables to the filling? Yes, feel free to add finely chopped bell peppers, onions, or even sun-dried tomatoes for extra flavor.
Can I make this into an appetizer with cremini mushrooms? Yes, the filling is great for mushroom appetizers. Simply keep an eye on them in the oven and adjust the cooking time as cremini mushrooms (baby bellas) are smaller and will cook faster.
Can I make this dish ahead of time? Partially, yes. You can prepare the stuffed mushrooms a few hours in advance and store them in an airtight container in the refrigerator. Just reheat in the oven before serving.
Is there a vegan version of this recipe? Yes, I use vegan Parmesan and mozzarella cheese to keep this dish plant-based.

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