Cut 1/8 inch thin strips of lemon peel from 1/2 of 1 lemon. Set aside. Slice other half and reserve for garnish. Squeeze juice from second lemon.
In small bowl, mix cornstarch and sugar. Add 2 Tbsp. lemon juice, chicken broth, sherry and soy sauce. Blend well. Set aside.
Heat large skillet or wok over medium high heat til hot. Add oil; heat til it ripples. Sprinkle chicken with salt and pepper. Stir fry 3 minutes or til chicken is cooked. Remove chicken to serving platter. Keep warm.
Add mushrooms, onions and red pepper to skillet. Stir fry 1 minute. Add lemon juice mixture to vegetables; stir fry 1 minute or til thickened. Return chicken to skillet and add lemon strips and stir fry 1 minute. Serve with hot cooked rice, if desired. Garnish with lemon slices. Serves 4