Clean chicken breasts and dry well. In a shallow baking dish, combine the flour, cayenne pepper, paprika, salt, and pepper. Dredge chicken breasts in flour mixture to coat. Shake off excess. In a large skillet heat 1/4-inch vegetable oil over medium heat. Add chicken and brown well, about 2 minutes on each side. Remove from pan and set aside. Pour excess oil from pan, leaving a thin layer. Add onions and garlic, saute, stirring occasionally, until translucent, about 3 to 5 minutes. In a bowl combine sour cream, chicken stock and green onions and mix well. Transfer chicken back to skillet, pour sour cream mixture over it. Bring to a simmer and cook, covered, until done, about 10 minutes.