Slice the tomato and onion thinly.
Cut the chicken breast into bite-sized pieces.
Heat olive oil in a pan and sauté the onion and chicken breast.
Add the tomato and season with salt and pepper.
Transfer the sautéed ingredients to an oven-safe dish and top with mozzarella cheese.
Bake in a preheated oven at 200°C for 10 minutes.