Remove all stems from cauliflower head and place in microwave safe bowl. Do not break up cauliflower. Add a few tablespoons of water to bottom of bowl. Cover with plate or plastic wrap, and cook on high for 10 minutes, until cauliflower is tender and cooked through.
Meanwhile, combine mayo, a generous tablespoon of mustard and Parmesan cheese in small bowl. Mix well.
Preheat oven to broil.
Remove cauliflower from bowl and place on baking sheet. Spread mayonnaise mixture over top and sides of cauliflower and sprinkle generously with paprika.
Broil until brown and bubbly, 2 to 3 minutes. Serve immediately.