Preheat oven to 350°F and grease a 9x13-inch baking dish.

Steam broccoli in a steaming basket over boiling water until just tender (about 4 minutes).

Make sauce by melting butter in a saucepan over medium heat. Stir in cream of mushroom soup, milk, minced garlic, onion powder, salt, and pepper until smooth.

Combine cooked rice, steamed broccoli, and sauce together in a large bowl until evenly coated.

Transfer mixture to prepared baking dish, spreading into an even layer.

Sprinkle breadcrumbs and extra shredded cheese on top.

Bake uncovered at 350°F for 20–25 minutes until cheese is bubbling and topping is golden brown.

Rest the casserole for 5 minutes before serving.