Heat oil in a Dutch oven over medium heat. Add cabbage, onion, and garlic; cook 12 minutes or until almost tender. Add broth, salt, pepper, and bay leaf; bring to a boil. Reduce heat, and simmer, uncovered, 12 minutes or until cabbage is tender. Slowly add polenta, stirring constantly with a whisk. Simmer 5 minutes or until thick. Discard bay leaf. Ladle soup into individual bowls, and sprinkle with cheese.