Rinse lentils, place in soup kettle, cover with 8 cups of water. let come to a boil. Add ham to lentils and cook slowly for 45 minutes, letting flavors develop. In separate pan, saute onion, celery, and carrot in oilve oil, add salt, pepper, tomatoes, and bay leaf. Cook for about 20 minutes. Add vegetable mixture to lentils; simmer for 10 minutes longer, until lentils and vegetables are tender. Serve with Parmesan cheese.