In a small bowl, stir together the soy sauce, peanut butter, vinegar, and cayenne pepper. Set aside.
Heat oil in a skillet or wok over high heat. Add chicken, garlic and ginger, and cook, stirring constantly, until chicken is golden on the outside, about 5 minutes.
Reduce heat to medium, and add green onion, broccoli, peppers peanuts, and the peanut butter mixture. Cook, stirring frequently, for 8 to 10 minutes, or until broccoli is tender, and chicken is cooked through.