Preheat the oven to 375 degrees F (190 degrees C). Place cauliflower into a 9x12-inch microwave-safe casserole dish or large bowl with water. Cover with microwave-safe plastic wrap and microwave on high power until half-steamed, about 5 minutes. Remove and pour out excess water but do not drain in a colander. Sprinkle cauliflower with mozzarella cheese, bacon, garlic, paprika, black pepper, salt, and red pepper flakes; toss to evenly distribute. Stir in mushroom soup until cauliflower is coated; spread mixture evenly in the dish. Top with French-fried onions, followed by Parmesan cheese. Bake in the preheated oven until golden and bubbly, about 45 minutes. Let stand for 5 minutes before serving.