Preheat oven to 350.
Combine the rice, spinach and butter. Place half of the mixture in a 2-qt. casserole dish.
Cover with oysters and season with salt and pepper. Top with remaining rice mixture.
Saute the mushrooms and onions in 2 Tbsp. butter. Once softened, remove them from the pan. Add in flour and cook for 2 minutes, careful not to brown the flour. Pour in the sherry and let cook for 30 seconds. Pour in the milk and whisk constantly until it thickens. Add the mushrooms back in and season to tastes. Add the sour cream and curry to the sauce and pour over rice and oysters.
Combine 2 Tbsp. melted butter with breadcrumbs. Sprinkle over top of dish.