Pat the tofu dry with a kitchen towel and cut it into bite-sized pieces.
Finely chop the onion and bell pepper.
Heat olive oil in a pan and sauté the onion and bell pepper.
Drain the oil from the canned tuna and add it to the pan. Stir-fry together.
Add the tofu and mix well, then season with salt and pepper.
Turn off the heat, transfer everything to a gratin dish, and top with shredded cheese.
Preheat the oven or air fryer to 200°C and bake for 10 minutes, or until the cheese is melted.