Preheat and prep: Heat your oven to 425°F (220°C).
Lightly grease a 9x13-inch baking dish or similar casserole pan.
Season the cauliflower: Toss the florets with olive oil, smoked paprika, garlic powder, a generous pinch of salt, and black pepper. Spread on a sheet pan.
Roast until golden: Bake the cauliflower for 18–22 minutes, stirring once, until the edges are browned and the centers are just tender. Don’t overcook; it will bake again later.
Mix the chicken and sauce: In a bowl, combine shredded chicken with 3/4 cup of the BBQ sauce.
Reserve the remaining 1/4 cup for drizzling.
Layer the bake: Add roasted cauliflower to the casserole dish. Scatter the red onion over it, then spoon the BBQ chicken evenly across. Sprinkle the cheddar and Monterey Jack on top.
Bake to melt: Reduce oven temperature to 400°F (205°C).
Bake uncovered for 10–12 minutes, until cheese is bubbling and lightly browned at the edges.
Add the “loaded” toppings: Remove from the oven. Drizzle with the reserved BBQ sauce. Sprinkle on the crumbled bacon and green onions.
Add optional ranch or jalapeños if you like a kick.
Rest and serve: Let it sit for 5 minutes so it sets slightly. Serve warm with a simple side salad or cornbread.