This is an approximation of a dish I ate at a Florence resturant, Maximillion.
Dice the onion.
Remove the peel of the grapefruit, section it, and then take the skins off each section. ( If you are going to arrange this recipe beautifully on a plate, try not to break the sections. Otherwise, don't worry about it.)
Slice the avocado into thin, long slices.
Now you can either throw all the diced, sectioned, and sliced ingredients into a bowl and douse it with a high quality olive oil (there really is a difference!) or arrange them beautifully (and integrated!) on a plate and douse each individual plate with olive oil. I would use about a cup of olive oil, more or less depending upon how much you love it, but always err on the side of more.
When you store it all together, the avocado won't get brown because of the acidic grapefruit juices!
This recipe is so good! Youd never think to combine these ingredients, but together they make a simple, but powerful, salad.