Sear the beef: Start by heating vegetable oil in a large cast iron skillet over high heat. Once the oil is shimmering and smoking, carefully add the beef chuck roast. Sear it on all sides until it develops a deep, rich brown crust. This step is crucial as it locks in flavors. Use tongs or two forks to rotate the meat, ensuring an even sear. Once browned, transfer the beef to your slow cooker.
Cook the beef: In the slow cooker, combine all remaining ingredients, including the low sodium beef broth, Coke, Worcestershire sauce, and seasonings. Stir well to combine. Layer the sliced onion on top of the mixture. Cover and set your slow cooker to low heat. Allow it to cook for at least 5 hours for a 3-pound roast or 6 hours for a larger roast. As it cooks, the beef will absorb all the lovely flavors.
Slice the beef and add veggies: After the cooking time is up, carefully remove the roast from the slow cooker. Let it rest for a few minutes on a cutting board. Once it’s cool enough to handle, slice the beef thinly across the grain. Return the sliced meat back to the slow cooker, adding the green bell peppers and cremini mushrooms. Give everything a good stir, ensuring the meat and veggies are submerged in the braising liquid. Cover and cook on low for an additional 45 minutes.
Toast the rolls: Preheat your oven to 400 degrees F. Split the hoagie rolls in half and lay them cut-side up on two large baking sheets. Toast the buns in the oven for about 5 minutes, or until they start to get golden and crisp. This step adds a delightful crunch to your sandwich.
Assemble the sandwiches: Spread a generous layer of spiced mayonnaise on both the top and bottom halves of each toasted roll. Layer the bottom halves with the beef and veggie mixture from the slow cooker. Place two slices of folded provolone cheese on top of the beef. If you have larger cheese slices, feel free to cut them in half to fit.
Melt the cheese: Return the baking sheets to the oven and keep the sandwiches open-faced. Bake at 400 degrees F for another 5 to 10 minutes, or until the cheese is beautifully melted and bubbling. The aroma will be irresistible!
Serve and enjoy: Remove the sandwiches from the oven and serve them immediately. For an extra treat, keep any remaining juices from the slow cooker to use as a dip for the sandwiches. Each bite is a flavor explosion!
