Melt margarine in heavy skillet. Add garlic and onions. Stir until blended. Cook over medium heat, until tender, for about five minutes. Remove from skillet.
Place chicken in skillet. Cook over medium heat until chicken is thoroughly done, about 12 minutes. Remove from skillet; keep warm.
Place frozen green beans, pepper, and cooked onions in same skillet. Cover and cook over medium-low heat until beans are tender, about five minutes.
Add chicken to vegetables. Continue cooking, stirring from time to time, until heated through—about three minutes.
Yields 4 servings.