Baked Hawaiian Sandwiches

INGREDIENTS

• 24 Hawaiian bread rolls (such as King's®), split
• 12 thin slices of honey-cured deli ham, halved
• 12 slices Swiss cheese, halved
• 12 thin slices deli smoked turkey, halved
• 12 thin slices provolone cheese, halved
• 1/2 cup butter
• 1/4 cup white sugar
• 1/4 cup dried onion flakes
• 2 tablespoons poppy seeds
• 1 tablespoon honey mustard