Start with the sauce: Heat the olive oil in a large pan. Saute the onion for 10 minutes. Add the garlic, cinnamon, lentils, tomatoes and water. Bring to a boil. Simmer until the lentils are tender (about 20 minutes). Cook the fettuccine according to package directions. Drain. Add the butter. Turn out into individual dinner plates. Top with the sauce. Serve.