Gently remove the stems from the mushroom caps and set aside. Scoop out the centers of the mushroom caps with a spoon to create more space for the filling.
Heat olive oil in a skillet over medium heat. Sauté the mushroom caps for 3-4 minutes on each side until they start to soften and release moisture. Remove from the skillet and set aside.
In a mixing bowl, combine the marinara sauce, mozzarella cheese, Parmesan cheese, cooked sausage or pepperoni (if using), and any other pizza toppings you desire. Season with salt and pepper.
Spoon the pizza mixture into each mushroom cap, packing it in generously.
Place the stuffed mushrooms on a baking sheet lined with parchment paper.
Bake for 15-20 minutes, or until the cheese is melted and bubbly and the mushrooms are tender.
Garnish with fresh basil (optional) and serve warm.
Notes
For an extra crispy top, sprinkle a little more Parmesan cheese on top of each stuffed mushroom before baking.
Make sure to remove excess moisture from the mushroom caps after sautéing to avoid soggy mushrooms.