Prep the oven and pan: Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with butter or oil.
Soften the cream cheese: Leave it at room temperature for 20–30 minutes, or microwave in short bursts until just spreadable.
Make the creamy base: In a large bowl, stir together cream cheese, sour cream, mayonnaise, ranch seasoning, garlic powder, onion powder, paprika, a pinch of salt, and pepper. Mix until smooth.
Add the cheeses: Fold in 1.5 cups of cheddar and all the mozzarella.
Reserve the remaining 0.5 cup cheddar for topping.
Add chicken and bacon: Stir in shredded chicken and most of the crumbled bacon. Save a small handful of bacon for garnish.
Optional veggie boost: If using broccoli, steam it lightly until crisp-tender and pat dry. If using cauliflower rice, sauté 3–4 minutes to remove moisture.
Fold into the mixture.
Assemble: Spread the mixture evenly in the prepared baking dish. Sprinkle the remaining cheddar on top.
Bake: Bake for 20–25 minutes, until the casserole is hot and the cheese is bubbling and lightly golden.
Finish and serve: Let it rest 5–10 minutes to set. Garnish with remaining bacon and sliced green onions.
Taste and adjust salt and pepper. Serve warm.