Preheat oven to 375 F. Line a baking sheet with parchment paper.
Stir mustard into the melted butter and set aside.
Fold a slice of turkey in half and place it on the wide end of the crescent. Top turkey with about a tablespoon of shredded pepper jack cheese. Roll up the crescent and place on baking sheet. Repeat for all crescent rolls and bake for 11-13 minutes, or until golden brown.
Remove crescents from oven and transfer to a cooling rack. Brush with butter and mustard mixture then immediately sprinkle with poppy seeds. It's best to work in batches of 2 or 3 so the butter does not begin to harden before you can add the topping.