Wash the flat-leaf parsley and basil, remove from the stems and cut into small pieces. Chop the pine nuts and walnuts into fine pieces. Peel the garlic and cut into fine pieces. Drain the tuna.
Put the olive oil in a pan and heat on medium heat. Put the garlic, pine nuts and walnuts in the pan at the same time (preferably mixed). Leave in the pan for about 1-2 minutes until the garlic is slightly translucent.
Add parsley and basil, tuna and tomatoes and stir. Season to taste with salt and pepper.