Heat oil in large skillet over medium-high heat. Add beef, breaking up with a spoon, and cook 5 minutes or until no longer pink. Add garlic, ginger and red pepper flakes. Cook 2 minutes, stirring. Add plum sauce, soy, lime juice and 1/3 cup water. Take off heat; keep warm.
Soak and cook noodles following package directions. Drain. Gently stir noodles and red pepper into beef mixture. Transfer to a medium-size bowl.
To serve, spoon beef mixture into lettuce leaves with some scallion and mint. Fold over to enclose. Squeeze with lime, if desired.