Remove stems and scrape out gills with a spoon. Pat caps dry with paper towels for 2 minutes. Brush each cap inside and out with 1 tablespoon olive oil. Sprinkle salt inside each cap.
4 portobello mushrooms, 3 tbsp olive oil, salt
Heat 1 tablespoon olive oil in a skillet over medium heat. Add diced onion and cook 3-4 minutes until softened. Add minced garlic and cook 30 seconds until fragrant. Toss in spinach and cook 2-3 minutes until fully wilted. Remove from heat.
1 onion, 3 tbsp olive oil, 3 cloves garlic, 2 cups fresh spinach
Transfer sautéed vegetables to a mixing bowl. Add breadcrumbs, half the cheese, chopped herbs, salt, and black pepper. Stir until evenly combined. Mixture should hold together when pressed but not be wet.
0.75 cup breadcrumbs, 1 cup shredded mozzarella or parmesan, 2 tbsp fresh parsley or thyme, salt, black pepper
Place mushroom caps gill-side up on a baking sheet. Fill each cap ⅔ full with stuffing mixture, pressing down gently. Top with remaining cheese. Avoid overfilling.
4 portobello mushrooms, 1 cup shredded mozzarella or parmesan
Bake at 375°F for 20-25 minutes until caps shrink slightly and filling turns golden brown. If topping isn’t crispy, broil for 2 minutes. Let rest 5 minutes before serving.
