In a bowl, mix the spinach, 1/2 cup Cheddar cheese, about 5 tablespoons dry bread crumbs, and the egg. Spread the mixture into the bottom of a small baking dish. Arrange the cod fillets on top of the spinach mixture, and season with salt and pepper. Top with the remaining Cheddar cheese and bread crumbs.
Cover, and bake 20 minutes in the preheated oven, or until fish flakes easily with a fork.