Microwave Scalloped Cauliflower

1 head cauliflower
1/2 cup mayo
1 tsp mustard
1/4 cup diced onion
3/4 cup grated cheese

Cook cauliflower in 1/4 cup water in deep bowl covered; covered on high for 9 minutes. Drain.

In small bowl mix mayo, mustard, and onion. Spread over cauliflower. Put cheese on top. Cover. Cook 2 minutes on high.