Preheat oven to 350º Fahrenheit and prepare a 9x13 baking dish with cooking spray.
Place the bottom parts of your rolls in the baking dish. Spread your Dijon mustard evenly on the bottom rolls.
Add ham slices, Two slices of ham over each roll, folded in half twice. Then, add one cheese slice per slider, folding it in half. Place the roll tops onto the cheese slices.
Combine your melted butter, onion powder, garlic powder, salt, and pepper in a small bowl. Brush evenly onto rolls. Top with poppy seeds.
Bake rolls for 20-25 minutes, top with fresh parsley.