Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the broccoli, cooked rice or quinoa, onion, garlic, and spices.
Add the sour cream, mayonnaise, and half of the cheddar cheese to the bowl, and mix until well combined.
Transfer the mixture to a greased 9x13 inch baking dish.
Top with the remaining cheddar cheese, and sprinkle breadcrumbs if using.
Bake in the preheated oven for 30–35 minutes, or until the top is golden and bubbly.
Allow the casserole to cool for 5-10 minutes before serving.