This easy Crockpot broccoli rice casserole is a side dish made with frozen chopped broccoli, instant rice, sweet onion, Velveeta, and cheddar. Broccoli cheese rice casserole is a dump-and-go slow cooker recipe with very little prep. The secret ingredient is frozen chopped broccoli. Chopped broccoli comes cut into very small pieces, much smaller than florets or broccoli cuts. This is a holiday classic, a great recipe for Thanksgiving or Christmas dinner.