1. Preheat the oven to 180 degrees.
2. Mash the tuna and mix it in the mixer until it reaches the dough consistency.
3. Put the tuna in a bowl, add the remaining ingredients and mix them with your hands. After adding salt and pepper to taste, form them into balls.
4. Spray both sides of the balls with cooking spray.
5. Grill each side for 4 minutes.
6. If you wish, you can grill the bread too. Spread pesto on bread, put the balls and add the onions and peppers.