Preheat the oven to 350 degrees F (175 degrees C). Grease a 3-quart baking dish.
Place broccoli and 2 tablespoons water in a large microwave-safe bowl; cover with plastic wrap and microwave on high for 5 minutes, stirring once. Drain.
Meanwhile, melt 1 tablespoon butter in a large skillet over medium heat. Add celery, onion, and garlic. Cook and stir until tender, about 3 to 5 minutes; add to broccoli in the bowl.
Stir in condensed soups, shredded cheese, milk, mustard, paprika, and pepper. Stir in rice until combined; spoon into prepared baking dish.
Combine panko with remaining 1 tablespoon melted butter; sprinkle evenly on top.
Bake in the preheated oven until browned and bubbly, about 30 to 40 minutes.
Notes
Add 1 cup chopped ham or cooked chicken to make this a more hearty main dish.