Preheat oven to 350°F (175°C).
Slice slider buns horizontally but keep them in one piece as a block.
Layer the bottom bun with sliced turkey breast evenly.
Place Swiss cheese slices over the turkey layer.
Cover with the top bun to form the slider sandwich block.
In a small saucepan, melt butter over low heat.
Stir in Dijon mustard, poppy seeds, garlic powder, and onion powder until well combined.
Brush the butter and mustard glaze evenly over the top of the slider buns.
Place the sliders in a rectangular baking dish.
Bake uncovered for 15 minutes until tops are golden brown and cheese is melted.
Remove from oven and cut into individual sliders before serving.