Step 1: Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.
Step 2: In a large skillet, melt the butter over medium heat. Add the rice and vermicelli mix from the Rice-A-Roni boxes and sauté until golden brown.
Step 3: Slowly stir in the water and the seasoning packets. Bring to a boil, then reduce heat to low, cover, and simmer for about 12-15 minutes, or until the rice is mostly tender but still has a slight bite.
Step 4: In a large mixing bowl, combine the cooked rice, shredded chicken, broccoli, cream of chicken soup, sour cream, garlic powder, pepper, and 1 cup of the cheddar cheese.
Step 5: Transfer the mixture into the prepared baking dish and spread it out evenly.
Step 6: Sprinkle the remaining 1 cup of cheddar cheese over the top of the casserole.
Step 7: Bake for 20-25 minutes until the cheese is melted and bubbling at the edges. Let it rest for 5 minutes before serving.