Heat oven to 350°F; line a 9-by-13-inch pan with parchment.

Slice connected rolls horizontally as one slab; place bottom slab in pan.

Layer ham and Swiss evenly to edges; replace top slab.

Whisk butter, Dijon, Worcestershire, poppy seeds, and onion powder; brush every roll.

Cover with foil; bake 15 minutes. Uncover; bake 5 to 7 minutes until centers reach 165°F and tops brown.

Rest 5 minutes; cut along seams into 12 sliders.