Prepare the Marinade: In a large bowl, whisk together the olive oil, balsamic vinegar, Worcestershire sauce, mustard, salt, pepper, onion powder, mustard powder, and minced garlic until well combined.

Marinate the Steak: Add the sliced steak to the bowl, ensuring it’s fully coated in the marinade. Cover the bowl and refrigerate for at least 1 hour, or up to 24 hours for deeper flavor. *Marinating is optional. If you don't have extra time you can skip the marinade. Marinating the beef makes it super flavorful.

Preheat your oven to 425°F

Place the sliced peppers, onions, and mushrooms on a large, rimmed sheet pan.

Add the marinated steak to the pan, pouring the remaining marinade over everything. Toss the vegetables to coat them evenly in the sauce.

Bake in the preheated oven for 15 minutes, or until the vegetables are tender and the steak is cooked to your liking.

Toast the Buns: If desired, spread garlic butter over the sandwich buns.

Switch the oven to broil and toast the buns for 1-2 minutes until golden brown. Watch closely to avoid burning.

Assemble the Sandwiches: Add the cooked steak and vegetables to the toasted buns. Layer slices of cheese over the filling.

Return the sandwiches to the oven under the broiler for another minute or two, just until the cheese is melted.

Serve the sandwiches warm and enjoy!