Preheat the Oven – Set your oven to 400°F (200°C).
Cook the Broccoli – Bring a large pot of water to a boil. Add broccoli and cook for 2-3 minutes until just tender but still crisp. Drain well.
Prepare the Sauce – In a mixing bowl, combine 1 cup of cheddar cheese, condensed soup, sour cream, milk, and seasonings (garlic powder, onion powder, dry mustard, pepper, and seasoned salt).
Assemble the Casserole – Stir in the drained broccoli and cooked chicken. Transfer the mixture to a 9×13-inch baking dish. Sprinkle the remaining cheese on top.
Make the Topping – Mix the melted butter with the breadcrumbs, then sprinkle evenly over the casserole.
Bake – Place in the oven for 18-20 minutes until the top is golden brown and the casserole is bubbling.
Serve – Enjoy on its own or over rice, pasta, or mashed potatoes.