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 to the pan and sauté together.
Season with salt and pepper to taste.
Place the sautéed ingredients into a gratin dish.
Top with tomato sauce and mozzarella cheese.
Bake in the oven at 200°C for 10 minutes.