Combine chicken and water in soup kettle. Bring just to a boil, reduce heat, cover, and simmer 45 minutes. Remove chicken, cool, discard skin, pull meat from bones, and chop. Set aside. Chill stock and skim fat from top. Return stock and chicken to kettle and heat to simmer. Add lentils and bay leaf and simmer, partially covered, 20 minutes. As lentils cook, melt butter in small skillet and sauté onions until tender. Add to chicken and lentils along with rice. Cover and cook slowly 20 minutes or until rice is tender. Remove bay leaf and season with salt and pepper.