1. Preheat the oven to 400F; spray a nonstick baking sheet. On a sheet of wax paper, combine flour, salt, and cayenne.
2. Separate the onion slices in rings, but keep them in groups of two, one ring inside another. Dredge the rings in the seasoned flour, dip in the egg whites, and then coat in the bread crumbs; place on the baking sheet. Bake on the top oven rack until bowned, about 10 minutes. Turn the rings over and baked until browned, 5-10 minutes.
6 rings per serving: 108 cal, 1 g fat, 0g sat fat,0g trans fat, 0mg chol, 330mg sod, 20g carb, 1g fib, 5g prot, 46mg calc.