In a medium bowl, mash the avocado until smooth, and then add the tuna.
Mix in the rest of the ingredients and serve immediately.
Tips:
If you want to prepare this salad in advance, to delay the browning of the avocado, add 1 teaspoon lemon juice to the salad, then place it in a container with the avocado pit and tightly cover the surface of the salad with plastic wrap.