Preheat oven to 375°F (190°C).
Lightly grease a 9×13-inch baking dish.
In a large bowl, combine:
cream cheese, sour cream, ranch dressing, black pepper.
Stir until smooth.
Fold in:
shredded chicken, bacon, green onions
1½ cups cheddar cheese
mozzarella cheese.
Spread the mixture evenly into the prepared baking dish.
Sprinkle the remaining ½ cup cheddar cheese over the top.
If using, combine crushed crackers with melted butter and sprinkle over the casserole.
Bake uncovered for 25–30 minutes, until hot and bubbly.
Let rest for 5 minutes before serving.