1. Clean the cauliflower and cut into as many pieces as you want in your casserole.
2. In a microwaveable dish place the cut up cauliflower.
3. Cover completely with water.
4. Cover the dish with a lid.
5. Microwave on high for approximately 10 minutes or until cauliflower is fork tender.
6. Drain water from cauliflower.
7. Mix mayonnaise and mustard together in a separate bowl making sure to mix well.
8. Pour mayonnaise and mustard mixture over cauliflower.
9. Sprinkle cheese on top.
10. Microwave uncovered on high until cheese is completely melted.
11. Mix together and serve.