Place sliced onion in a medium nonstick skillet coated with cooking spray. Cover and cook over medium heat 10 minutes or until onion is limp and golden, stirring occasionally. Reduce heat to low, and add 1/4 cup chili sauce and grape jelly. Cover and cook 5 minutes or until onion is tender and thoroughly heated.
Combine beef and next 5 ingredients in a bowl; stir well. Divide mixture into 4 equal portions, shaping each into a 1/2-inch-thick patty. Prepare grill or broiler. Place patties on grill rack or broiler pan coated with cooking spray, and cook 4 minutes on each side or until done.
Line the bottom halves of buns with a lettuce leaf; top each with a patty, 1/4 cup onion mixture, and top half of bun.