Preheat oven to 350°F (175°C).

Melt butter in a saucepan over medium heat.

Add minced onion and celery to the saucepan and sauté until softened.

In a large bowl, combine the cooked rice, sautéed onions and celery, frozen minced broccoli (thawed), cream of mushroom soup, drained and chopped water chestnuts, and cubed Velveeta cheese.

Mix all ingredients thoroughly until well combined.

Pour the mixture into a greased 9x13 inch casserole dish.

Cover the casserole dish with aluminum foil.

Bake in the preheated oven for 25-30 minutes, or until heated through and the cheese is melted and bubbly.

Let cool slightly before serving.