This is one of my favorite ways to serve avocado. Many people think this fruit (it's technically not a veggie) is unhealthy, but not so! See More on Avocados.
Avocados come in many types, shapes and colors. How can you tell what to choose? See California's Avocados for tips.
1 large avocado
Peel garlic clove. Put in a mortar & pestle with the salt and pound until a thick past forms. If you don't own a mortar & pestle, place the salt on a cutting board with the chopped garlic clove on top. With the side of a large chef's knife, flat meat tenderizer or anything else hard and flat, grind and mash into a paste. Place in a salad bowl.
Chop the onion very fine or slice very fine. Add to garlic mixture with oil and vinegar. Stir well, cover and set aside for a while (if more than 15 minutes or so, refrigerate). Just before serving, cut the tomato into cubes and lay out on a paper towel to drain. (I do NOT seed the tomatoes. They are extremely healthy - see Tomato Seeds & Clot Prevention. It's the juice, in any case, that changes the flavor and can be drained off easily.
Peel the avocado as and cut into cubes. Immediately add to the vinegar-oil mixture and stir to coat so the avocado won't turn brown. Add the chopped tomatoes and mix lightly. Serve on a bed of lettuce, with freshly ground black pepper if you wish.