Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the thousand island dressing, garlic powder, onion powder, and black pepper. Whisk well to combine.
In the prepared baking dish, layer half of the cubed rye bread at the bottom.
Spread half of the sauerkraut over the bread, followed by half of the corned beef.
Drizzle half of the dressing mixture over the layers, and sprinkle half of the shredded Swiss cheese on top.
Repeat the layering process with the remaining rye bread, sauerkraut, corned beef, dressing mixture, and finish with the remaining Swiss cheese.
Pour the melted butter evenly over the top of the bake.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes.
After 30 minutes, remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden.
Allow the bake to cool for a few minutes before slicing and serving.