Preheat oven to 350°F (175°C).

Grease a baking sheet or dish.

Without separating the sweet rolls, slice each package of rolls horizontally to create a top and bottom half.

Place the bottom halves of the rolls onto the prepared baking sheet.

Layer the ham evenly over the bottom rolls.

Arrange the Swiss cheese slices over the ham.

Place the dill pickle slices evenly over the cheese.

Top with the top halves of the sweet rolls.

In a microwave-safe bowl, melt the butter.

Stir in the finely chopped onion and Dijon mustard into the melted butter.

Drizzle the butter mixture evenly over the top of the rolls.

Cover the sliders with foil.

Bake for 10 minutes covered.

Remove the foil and bake for another 5-10 minutes, or until golden brown and heated through.