Place the cauliflower in a large saucepan with just enough water to cover. Bring to a boil, and cook until fork tender, about 5 minutes. Drain, and coarsely chop or break up with a fork.
Preheat the oven to 350 degrees F (175 degrees C). Coat a large casserole dish with cooking spray.
Melt butter in a saucepan over medium heat. Cook onion in the butter until tender, but not browned. Stir in the Cheddar cheese soup, milk, shrimp, mushrooms and parsley. Season with cayenne pepper, black pepper, and Creole seasoning. Heat for a minute on low to blend the flavors.
Place the cauliflower into the prepared baking dish. Pour the contents of the saucepan over the cauliflower, and stir slightly to blend.
Bake for 20 minutes in the preheated oven, until bubbly. Sprinkle with paprika just before serving.
