From "The Complete Book of Greek Cooking," edited by Katherine R. Boulukos (Harper-Collins). In a large skillet, brown lamb shanks in oilve oil. Add 1/2 cup water, garlic, 1/2 teaspoon salt, oregano and pepper. Cook, covered, over low heat for one hour, or until tender. Rinse lentils and drain. In a medium saucepan, combine lentils, 3 cups water, onion, celery, bay leaf and 1-1/2 teaspoons of salt. Simmer, uncovered, 50-60 minutes, or until vegetables are tender. Pour mixture into greased baking dish. Top with meat, lemon slices. Bake 20-25 minutes, until liquid is absorbed and lentils are tender. Discard onion and bay leaf.