Season the chicken with salt and pepper.
Heat 1 T. peanut oil in a large non-stick pan or wok. Add half the chicken and stir constantly until cooked through - about 4 minutes. Transfer the chicken to a plate using a slotted spoon.
Cook remaining chicken and add to plate.
Heat remaining peanut oil and sauté peppers and onions until tender - about 4 minutes.
Reduce heat to medium, add the ginger, garlic and red pepper flakes and stir for 1 minute.
Mix the cornstarch and water in a small bowl. In the pan, stir in the cornstarch mixture, vinegar and soy sauce. Remove from the heat. Return chicken to pan and stir.
Serve with lettuce leaves and peanuts.