Creating Chicken Broccoli Casserole is a straightforward process. Follow these steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Prepare Broccoli: Steam or blanch the broccoli florets until just tender, about 3-5 minutes. Drain and set aside.
3. Mix Ingredients: In a large bowl, combine the cooked chicken, steamed broccoli, cream of chicken soup, sour cream, cheddar cheese, cooked rice, garlic powder, salt, and pepper. Mix until well combined.
4. Transfer to Baking Dish: Spoon the mixture into a greased 9×13 inch baking dish, spreading it evenly.
5. Prepare Topping (optional): If using breadcrumbs, mix them with olive oil in a small bowl until coated. Sprinkle the mixture over the casserole.
6. Bake: Place the baking dish in the preheated oven and bake for 30-35 minutes or until the casserole is bubbly and the top is golden brown.
7. Cool: Remove from the oven and allow it to cool for 5-10 minutes before serving.

These steps will guide you in creating an incredible Chicken Broccoli Casserole effortlessly.