Cut paper-think slices of spring onion to make 1 loose cup. Finely chop cilantro leaves to make 1/2 C. Toss both together with half the vinagrette.
Use a vegetable peeler or very sharp knife to cut 3 summer squash into very thin slices. Cut the slices into 2 inch pieces. Place in a bowl, salt well, and allow to sit for 10 minutes. Remove the squash from the bowl and add to the onion/grapefruit/cilantro.
Toast 1/2 C. pumpkin seeds. Crumble 1/2 C. feta cheese.
Serve the salad over washed and dried arugula and top with the pumpkin seeds and feta. Drizzle with additional vinagrette to taste.