Finely chop the onion and bell pepper.
Heat olive oil in a pan and sauté the onion and bell pepper.
Cut the chicken breast into small pieces, add to the pan, and stir-fry together.
Add tomato sauce and bring to a simmer.
Place the soft tofu in an ovenproof dish and pour the sauce over it.
Sprinkle mozzarella cheese on top.
Bake in the oven at 200°C for 10 minutes to finish.