Preheat the oven. Set to 375°F (190°C). Grease a 9x13-inch baking dish.
Cook the bacon. In a skillet over medium heat, cook chopped bacon until crispy. Transfer to a paper towel-lined plate.
Reserve 1 tablespoon bacon fat.
Prepare the base. If using pasta, boil in salted water until just al dente. Drain well. If using cauliflower, steam until barely tender, then pat dry to prevent excess moisture.
Warm the broccoli. Lightly steam or microwave until bright green and slightly tender.
Pat dry.
Make the sauce. In a large bowl, whisk together ranch dressing, sour cream, cream cheese (softened helps), garlic powder, onion powder, black pepper, and smoked paprika. Stir until smooth and creamy.
Combine the mix-ins. Add cooked chicken, half the bacon, broccoli, and pasta (or cauliflower) to the sauce. Fold gently to coat.
Taste and adjust salt if needed.
Layer the cheese. Stir in half the cheddar and half the mozzarella. Spread the mixture evenly in the baking dish. Top with remaining cheeses and the rest of the bacon.
Bake. Bake uncovered for 18–22 minutes, until the casserole is bubbling and the top is lightly golden.
Finish and serve. Let rest 5–10 minutes so it sets a bit.
Sprinkle with parsley or chives. Serve warm.