Avocado with Grapefruit and Sweet-Onion Salsa

Cut off both ends of grapefruits, and remove the peel, pith, and outer membranes, following the curve of the fruit with a paring knife. Working over a bowl to catch the juices, use the knife to carefully slice between the sections and membranes of each grapefruit to remove the segments. Slice each grapefruit segment into small pieces, and set aside.

Place onion in a small bowl. Squeeze remaining juice from grapefruit membranes over onions, and let stand 20 minutes to soften. Pour off and discard juice, and add grapefruit segments and cilantro. Add enough reserved grapefruit juice to moisten. Season with salt. To serve, place 3 to 4 tablespoons on each of the avocado halves.