Place beef and sweet chili sauce in medium bowl; marinate for 1 hour.
Heat oil in large skillet over medium-high heat. Add beef and marinade, chopped onion, garlic and chile; cook, stirring frequently, until beef is no longer pink. Cut head of lettuce in half and carefully separate leaves.
Spoon beef mixture into lettuce cups; top evenly with green onions, cilantro and peanuts.
Servings: 4