Wash and dry the tomatoes and mint leaves. Cut the tomatoes in half, remove the seeds, and cut the tomatoes into 5 cm cubes. Chop the mint leaves, but leave some to garnish the salsa. Chop the walnuts finely.
In a bowl, mix the tomatoes with mint, add the olive, lemon juice, salt, and pepper. Add the walnuts and mix well. Garnish with mint leaves.