Cut the tofu into bite-sized pieces.
Finely chop the onion and bell pepper.
Heat olive oil in a pan and sauté the onion and bell pepper.
Add the tofu and stir-fry for a bit longer.
Season with salt and black pepper.
Put the sautéed ingredients into an oven-safe dish and pour tomato sauce over them.
Top with mozzarella cheese.
Bake in a preheated oven at 180°C (356°F) for 10-15 minutes.