Preheat your oven to 425 degrees. In a small bowl mix together mayo and mustard, set aside.
Using a 9x13 baking dish, lay bottom layer of the slider buns. spread half the mayo/mustard mixture on top of the buns. Add 6 cheese slices across the top, add the turkey, add the ham, and add the remaining cheese. Next spread the remaining mayo/mustard across the top of the cheese, and top with slider bun tops.
Using a pastry brush (or you can just drizzle), brush the melted butter on top of the buns liberally. Sprinkle grated cheese and poppy seeds across the top.
Cover with foil, place into oven and bake for 15 minutes. Remove foil and bake an additional 5 minutes. Carefully remove from oven, let cool for a few minutes. Use a knife to cut the sliders and then serve.