Heat the oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish with butter or oil.
Prep the bacon and broccoli. Cook bacon until crisp, then crumble.
Steam or blanch broccoli just until bright green and slightly tender; drain well.
Make the creamy base. In a large bowl, mix cream cheese, sour cream, mayonnaise, ranch seasoning, garlic powder, onion powder, smoked paprika, black pepper, and heavy cream if using. Stir until smooth.
Add the chicken and veggies. Fold in the shredded chicken, broccoli, half the bacon, half the green onions, 1 cup cheddar, and all the mozzarella. Taste and add salt only if needed.
Assemble the casserole. Spread the mixture into the prepared dish.
Top with the remaining cheddar and the rest of the bacon.
Bake until bubbly. Bake for 18–22 minutes, until the edges are bubbling and the cheese is melted and golden in spots.
Finish and serve. Let it rest 5–10 minutes so it sets. Sprinkle with remaining green onions and serve warm.