Finely chop the onion and bell pepper.
Heat olive oil in a pan and sauté the onion and bell pepper.
Add spicy tuna and corn kernels, and stir-fry for 2 minutes.
Transfer the sautéed mixture into an oven-safe dish.
Evenly sprinkle mozzarella cheese on top.
Bake in a 180°C oven for 10 minutes.