For sauce, in a small bowl combine water, soy sauce, dry sherry, cornstarch, and hot pepper sauce; set aside.
Add oil to wok or 12-inch skillet. Preheat over medium-high heat (add more oil if necessary during cooking). Stir-fry garlic and ginger in hot oil for 15 seconds. Add leeks and, if desired, chili peppers. Stir-fry for 1-1/2 minutes or until leeks are crisp-tender. Remove leek mixture from wok. Add half of the chicken to wok. Stir-fry for 2 to 3 minutes or until no longer pink. Remove chicken from wok. Repeat with remaining chicken. Return all chicken to wok; push chicken from center of wok.
Stir sauce; add to center of wok. Cook and stir until thickened and bubbly. Return cooked vegetables to wok. Stir to coat. Cook and stir about 1 minute more or until heated through. Stir in peanuts. Serve immediately over cooked rice. Makes 4 servings.