Prepare the Ingredients: Thinly slice the onion. If using, heat the cheese sauce gently until warm. Preheat the oven to 350°F (175°C).

Cook the Onions: In a large skillet, melt butter over medium heat. Add sliced onions and cook until caramelized, stirring occasionally, about 10 minutes. Remove onions from the skillet and set aside.

Cook the Beef: In the same skillet, add vegetable oil and increase heat to high. Add thinly sliced beef, season with garlic powder, salt, and pepper. Cook until the beef is browned, about 5 minutes.

Assemble the Sandwiches: Slice hoagie rolls and lay them open on a baking sheet. Evenly distribute the cooked beef onto each roll. Top with caramelized onions.

Add Cheese: Place slices of cheddar cheese on top of the beef and onions. Optionally, add warmed cheese sauce over the top. Add jalapeños, if using.

Melt the Cheese: Place the sandwiches in the oven and bake until the cheese is melted and bubbly, about 5-7 minutes.

Serve: Remove from oven, close the rolls, and serve immediately.