In a large skillet heat 2 tbsp. of vegetable oil over medium heat. Add the sliced onion and cook until caramelised , about 10 minutes, then add mushrooms, green bell pepper and season with salt. Cook another 5 min, stirring from time to time. Keep aside.

In a large skillet heat the remaining 2 tbsp. of oil, then add the thinly sliced steak and spread in an even layer. Cook until brown undisturbed, then stir and season with salt and pepper. Cook steak until it is done or reaches desired doneness, about 5 minutes.

Divide into 4 even portions and blanket each with 1-2 slices of Longhorn Pepper Jack cheese. Cover the skillet with the lid and turn off the heat so the cheese will melt without overcooking the meat, about 2- 3 minutes.

In a small bowl mix together garlic and butter.

Slice sandwich buns 1/2 through.

Spread garlic butter onto the cut sides of 4 sandwich buns.

Toast buns in a pan on the stove. In a a heavy-bottomed pan over medium-high heat, cook buns for a couple minutes on each side, or until golden brown.

Stuff each bun with the sautéed veggies and top with cheesy steak, then layer mayonnaise, if desired.

Serve immediately.