Spread a thin layer of butter on the cut side of the Hoagie buns all the way to the edges.

Heat a large lidded nonstick skillet between medium to medium-high heat (you’ll use the lid later). Place the buns buttered side down and toast until golden brown. Check after a minute, then monitor every 10 seconds until they’re golden brown. Remove the buns from the pan, and set aside. You can cover them with a clean kitchen towel to keep them warm if you'd like.

Add the Tablespoon of butter to the pan, and swirl to melt and coat the bottom of the pan. Add the onions and saute until they start to turn translucent (about 4 minutes), then move them over to one side of the pan.

Next, add the ground beef to the pan as one large hamburger patty. Season the top side with half of the garlic powder, salt, and pepper. Allow the beef to sear for 3-4 minutes, then flip over and sear for another 3 minutes.

Begin to chop the beef up into chunks, using the bottom edge of a spatula. Once broken up, sprinkle the remaining salt, pepper, and garlic powder over the beef, and start mixing in the onions. Continue to cook until the beef is no longer pink (about 5 minutes). Drain off and discard the grease, then return the skillet back to the stove.

Divide the beef and onions into 2 long equal portions in the pan that match the width and shape of the bun.

Remove the pan from the heat, then place 4 slices of American cheese on top of each mound, cover with a lid, and let it rest until the cheese has fully melted (about 2 minutes).

Spread mayo on both the top and bottom sides of the buns. Spread half of each mound of beef on the bottom half of one bun, top with lettuce and tomato, then add ketchup to the top half. Repeat with the remaining buns.