Slice hoagie rolls 3/4 of the way through with a serrated knife. Dice onions and thinly slice beef.

In a small bowl, stir together 2 Tbsp softened butter with 1 pressed garlic clove. Spread garlic butter onto the cut sides of 4 hoagie rolls. Toast the buns on a large skillet, flat cooktop or griddle on medium heat until golden brown, then set aside.

Add 1 Tbsp oil to your pan/cooktop and sauté diced onions until softened. Sprinkle lightly with salt and cook until caramelized, then transfer to a bowl.

Increase to high heat and add 1 Tbsp oil. Spread the super thinly sliced steak in an even layer. Let brown for a couple of minutes undisturbed then flip and season with 1/2 tsp salt and 1/2 tsp black pepper. Sauté until steak is fully cooked through, then stir in the caramelized onions.

Divide into 4 even portions and top each with 2 slices of cheese. Turn off the heat so the cheese will melt without overcooking the meat.

Spread a thin layer of mayo on the toasted side of each roll. Working with one portion at a time, place a toasted bun over each portion and use a spatula to scrape the cheesy beef into your bun as you flip it over. Serve warm.