01 - Preheat oven to 375°F and grease a 9x13-inch baking dish with butter or cooking spray.
02 - Bring a large pot of salted water to a boil. Add cauliflower florets and cook for 4 minutes. Add pasta and cook both together for 5–6 minutes, until pasta is al dente and cauliflower is just tender. Drain thoroughly in a colander and set aside.
03 - In a medium saucepan, melt butter over medium heat. Whisk in flour to form a smooth roux; cook for 1–2 minutes, stirring constantly until bubbling but not browned.
04 - Slowly whisk in milk, stirring constantly to prevent lumps. Continue cooking for 4–5 minutes until sauce thickens and coats the back of a spoon. Remove from heat.
05 - Stir in shredded cheddar, mozzarella, Parmesan, garlic powder, onion powder, smoked paprika, salt, and pepper until completely smooth and melted.
06 - Pour the cooked pasta and cauliflower into the cheese sauce. Mix thoroughly to coat evenly, then transfer the mixture to the prepared baking dish.
07 - In a small bowl, combine breadcrumbs with Parmesan cheese and olive oil. Toss until evenly mixed.
08 - Sprinkle the breadcrumb mixture evenly over the top of the dish. Bake for 20–25 minutes until the sauce is bubbling and the topping is golden brown. Let rest for 5 minutes before serving.