1) Cut the top and bottom off of the oranges and the grapefruit to make a stable cutting surface. Place fruit flat on cutting board, and using a sharp knife, slice down on the sides to remove the peel and white pith. Dice the whole orange, but section the grapefruit: holding the fruit in your hand, gently cut the grapefruit along the sides of the membranes to get wedges of grapefruit out without the membranes.
2) Combine all ingredients in a bowl, except avocados and cilantro, and toss gently. Just prior to serving, cut and add the avocado and cilantro; combine well. Enjoy!