Here are two things Fi and I did with avocado this week (I was more of a consultant but definitely at least an executive consultant):
Proportions are up to you, though I would not over do it on the grapefruit, the grapefruit is there to add a delicious tartness but not overwhelm the essential avocadoness of this. I recommend only a small amount of olive oil, drizzled via a spoon in order to control the flow and amount. Cut the avocado and grapefruit up into similar sized cubes, and slice the tomato (then slice again, so they are thinner than the avocado pieces but maybe a little longer). No need to put anything on the toast, though you can add a little olive oil if you like.