Preheat the oven to 350°F (175°C).
Slice the slider buns in half horizontally and place the bottom halves in a baking dish.
Spread Dijon mustard evenly over the bottom buns.
Layer the ham slices over the mustard.
Place Swiss cheese slices on top of the ham.
Add pickles if desired for extra flavor.
Place the top halves of the buns on the cheese.
Brush melted butter over the tops of the buns.
Sprinkle poppy seeds on top for added crunch.
Cover the baking dish with foil and bake for 15 minutes.
Remove the foil and bake for an additional 10 minutes until golden brown.