Pound chicken breasts with meat mallet. Coat chicken with flour; season with salt and pepper. Melt margarine in large skillet. Add chicken and garlic. Cook over medium heat until chicken is tender on all sides. Remove chicken to serving platter; keep warm. Add lemon juice to skillet, scraping drippings from bottom of pan. Bring to boil; boil 1 minute or until slightly thickened. Stir in parsley. Pour sauce over chicken. Garnish with lemon slices.