Heat a large skillet over medium heat. Add the butter and let melt. Add the onions and a pinch of salt and cook, stirring occasionally, until softened and caramelized, about 5 minutes. Transfer the onions to a plate and reserve.
Increase the heat to medium high. Add the beef to the skillet with the onion drippings and season liberally with salt and pepper. Cook, without stirring, until browned, about 3 minutes per side. Break up the beef with a wooden spoon or spatula.
Add the onions on top of the browned beef, then top with the cheese. Fill the rolls with the meat mixture. Get lots of napkins and eat!!
For more ingredient substitution ideas, see the article below.