Bring water and chicken bouillon granules to a boil in a stock pot, stirring to dissolve bouillon. Place ham bone in boiling broth, reduce heat to medium-low, and stir in lentils. Simmer until lentils begin to soften, about 10 minutes.
Stir celery, carrots, green bell pepper, onion, marjoram, and bay leaf into broth and simmer until lentils and vegetables are tender, 10 to 20 minutes. Turn off heat and remove ham bone from soup. Cut ham from the bone, cube the meat, and return meat to soup, discarding the bone.