Separate onion rings, place half on microwave-safe plate and sprinkle with 1 Tbsp. water. Cover with wax paper and microwave on HIGH 1 minute. Repeat with remaining onions, pat dry and cool.
Combine onion rings and egg whites in large bowl. In sealable plastic bag, combine flour, cornmeal, salt, pepper and chili powder. A few at a time, place onion rings inside bag and shake well. Shake off excess flour and place each ring single layer on parchment-lined baking sheet.