Preheat oven to 350°F. Grease a 9x13 inch baking dish.
Heat olive oil in a skillet over medium-high heat. Season chicken with salt, pepper, garlic powder, and onion powder. Sear the chicken until lightly browned (it doesn’t need to be fully cooked). Remove and set aside.
In the same skillet, sauté the diced onion until softened, about 3-4 minutes. Add minced garlic and cook for another 30 seconds.
In a large bowl, combine the cream of chicken soup, sour cream, milk, chicken broth, and uncooked rice. Stir in the sautéed onion and garlic, broccoli florets, 1 1/2 cups of shredded cheddar cheese, and the seared chicken.
Transfer the mixture to the prepared baking dish and spread evenly.
Cover tightly with foil and bake for 50 minutes.
Remove the foil, stir the casserole, and top with the remaining 1 cup of cheddar cheese. Return to the oven uncovered and bake for an additional 10-15 minutes, until the cheese is melted and bubbly.
Let it rest for 5 minutes before serving.