Preheat oven to 350ยบ F. Lightly butter or spray a 9x13 baking dish. Split open the rolls and place the bottom half of the rolls into the prepared baking dish.
Layer half of the ham, the spinach, cheese, and the remainder of the ham on the bottom of the roll and top with the top of the roll.
Whisk together all the butter, mustard, poppy seeds, dried onions, and Worcestershire sauce (or coconut aminos) until well combined to create the sauce. Pour the sauce over the top of the rolls and bake until the cheese has melted and the tops of the sandwiches are golden brown, about 15 to 20 minutes. Serve warm.