While rice is cooking, cut 1/8-inch-thick strips of lemon peel from half of 1 lemon. Set aside. Slice other half and reserve for garnish. Squeeze juice from second lemon. In small bowl, combine cornstarch and sugar. Add 2 tablespoons lemon juice, broth, sherry and soy sauce; blend well. Set aside.
Heat oil in large skillet or wok over medium-high heat until hot. Add chicken; sprinkle with salt and pepper. Cook and stir 3 to 4 minutes or until chicken is no longer pink. Remove from skillet; cover to keep warm.
Add onions, bell pepper and mushrooms to skillet. Cook and stir 1 minute. Add lemon juice mixture to vegetables; cook and stir 1 to 2 minutes or until thickened. Return chicken to skillet; add lemon strips. Cook and stir 1 minute. Serve with rice. Garnish with lemon slices.