Got the recipe for this delicious avocado and ruby grapefruit salad from The Three Ingredient Cookbook by Jenny White.
All it is, is one sliced avocado, one sliced grapefruit and arugula lettuce. You squeeze the grapefruit skin (after cutting out the slices) to get the juice for the dressing. Mix the juice with salt, a dash of chili powder (or chili oil) and a splash of olive oil. I realize that's more than 3 ingredients, but the book's philosophy seems to be that if you should already have something, like salt, then it doesn't count as an ingredient.