If using wooden skewers, soak according to package directions. Lay flank steak flat and cut into 1/4″ slices across the grain. Set aside.
Whisk together remaining ingredients. Add sliced beef and toss to completely coat each piece. Allow to marinate in the refrigerator for 3-4 hours.
Preheat grill to medium high. Thread beef slices onto skewers. Spray grills with non stick spray if desired to prevent beef from over sticking to the grills.
Grill beef skewers for approximately 7-8 minutes, turning once or twice to crisp up the edges. Serve with peanut sauce.
Peanut Sauce
Combine all ingredients in a small saucepan and warm over medium heat. Do not boil or the peanut butter will separate. Garnish with additional chopped peanuts and serve with beef skewers.