Preheat the oven to 200°C (392°F).
Spread tomato sauce over the tortilla.
Drain the oil from the canned tuna and evenly distribute the tuna over the tortilla.
Thinly slice cherry tomatoes and onion, then place them on top.
Add basil leaves and mozzarella cheese.
Drizzle a little olive oil.
Bake in the oven for 10 minutes.