Sprinkle chicken with 1/4 teaspoon salt and 1/4 teaspoon pepper. Coat a nonstick skillet with cooking spray. Place over medium-high heat until hot. Add chicken to skillet, and cook 5 minutes on each side or until browned.
Add onion, mushrooms, and red pepper. Sprinkle with remaining 1/4 teaspoon salt, 1/4 teaspoon pepper, and marjoram; add vermouth. Bring to a boil; cover, reduce heat, and simmer 10 minutes. Stir in sour cream; cover and cook 5 additional minutes. Uncover and cook 10 minutes or until chicken is done and sour cream mixture is slightly thickened, stirring occasionally.