Prepare 9 x 13 baking dish or pan by placing parchment paper in bottom. You can also butter or spray the dish as well. Preheat oven to 350°.
Place bottom of the rolls in the dish.
Add ½ of the cheese on top of bottom rolls. Then layer corned beef slices on top of the cheese. Top with remaining cheese slices.
Next place sauerkraut on top of cheese and then spoon thousand island dressing on top.
Cover with the top half of the buns.
In a mixing bowl add melted butter, dijon mustard, minced onion, garlic powder, and poppy seeds and stir until combined.
Using a silicone brush mixture over tops of the rolls.
Cover with foil and bake for 15-20 minutes or until cheese is melted. Remove foil and bake until tops are golden brown.
Remove from oven and cut into individual sliders and place on a plate or serving dish and serve warm.