Remove peel and pith from 1/2 grapefruit and 1 small navel orange. Working over a bowl, cut out grapefruit and orange segments then squeeze juice from membranes. Place 2 cups baby arugula on a platter and top with 1 ripe sliced avocado, 1 sliced radish and citrus segments with juices, Drizzle with 1 tablespoon extra-virgin olive oil and top with 1 thinly sliced scallion. Season with coarse salt and freshly ground pepper and serve.
