Sandwich Build: For the glaze, add the orange peel, bourbon, cherry juice and some black pepper to a small saucepan. Simmer until reduced to 1/4 cup, about 10 minutes. Your pot may flambe from the bourbon, don't worry- just wait until the alcohol burns off. Once reduced, turn off the heat and whisk in the butter.
Sprinkle the steak liberally with salt and pepper. Heat a cast-iron pan over medium-high heat. Add a light coat of oil and place the steak in the pan. Cook the steak almost to desired doneness, depending on thickness, 3 to 5 minutes per side. Turn off the heat and glaze the steak on all sides in the pan while flipping. Remove the steak from the pan to rest.
For the sandwich build: Pile some Bourbon Creamed Spinach on the bottom piece of the pretzel roll. Thinly slice the steak against the grain and place on top of the spinach. Top with some red onions and finish with the top of the roll. Repeat for the remaining sandwiches.
For the Bourbon Creamed Spinach, strain the thawed spinach in a colander and squeeze liquid out with a towel. Melt the butter in a large straight-sided skillet over medium heat. Add the garlic and onions, season with salt and pepper and cook until onions are softened, about 5 minutes. Turn off the heat and add the bourbon. Stir to combine, turn heat back on to medium and simmer 1 minute. Add the cream, and cook until the cream is reduced by half, about 5 minutes. Stir in the cheese and cook until melted, and then mix in the spinach to combine. Cover and cook over low heat until the spinach is tender, 8 to 10 minutes, and then season with salt and pepper.