Wrap the tofu with a kitchen towel to remove excess moisture, then cut it into bite-sized pieces.
Finely chop the onion, bell pepper, and mushrooms.
Heat olive oil in a pan and sauté the onion, bell pepper, and mushrooms.
Add the tofu and stir-fry together, seasoning with salt and pepper.
Transfer the sautéed ingredients to an oven-safe dish and spread tomato sauce on top.
Evenly sprinkle mozzarella cheese over the dish.
Bake in a preheated oven at 180°C (356°F) for 10 to 15 minutes, until the cheese is melted.