Place the cauliflower and 1 cup water in a covered dish and microwave on high until tender, about 5 minutes. Meanwhile, melt the margarine in a 4 1/2 quart Dutch oven or soup pot over medium heat. Add the onions, garlic and Worcestershire and stir well. Add the beer. Raise heat to high and boil 3 minutes to evaporate the alcohol. Add the chicken broth and bring the soup back to a boil. Lower the heat to medium and boil while you drain the cauliflower, chop it into bite-sized pieces and add it to the pot. Combine the cornstarch and 3 tbsp. water in a small container that has a lid. Shake until the lumps disappear, then set aside. Add the half-and-half and cheese to the soup. Stir constantly until the cheese melts, then shake the cornstarch mixture again and add it to the pot. Stir constantly until the soup is thick, about 2 minutes. Serve garnished with bacon bits (if using).