Hawaiian Roll Roast Beef and Cheese Sandwiches

Name: Hawaiian Roll Roast Beef and Cheese Sandwiches
Prep time: 15 min
Cook time: 40 min
Total time: 55 min
Cuisine: American
Ingredients: 0.5 cup prepared horseradish; 1 (12 count) package Hawaiian bread rolls, split; 12 slices deli roast beef; 12 slices deli-sliced Swiss cheese; 0.5 cup butter; 1 onion, finely chopped; 2 tablespoons brown sugar; 1 tablespoon spicy brown mustard; 1.5 teaspoons Worcestershire sauce; 1 pinch garlic powder, or to taste; 2 teaspoons poppy seeds