Sauté the beef in a large skillet for 5 minutes, until no longer pink. Stir in rice, sugar, pepper flakes, onion, mint, cilantro, lemon juice, soy, sesame oil, salt and pepper. Heat through, stirring frequently. Spoon into serving dish; set on a large platter. Surround dish with lettuce and mint leaves.
To serve, have guests spoon a small amount of beef mixture and mint onto a lettuce leaf; roll up and eat out of hand.