Begin by melting 1 tablespoon of salted butter in a skillet over medium heat. Carefully place the hoagie rolls cut-side down in the skillet, toasting them for about 2-3 minutes until golden brown and crispy.

In the same skillet, add the remaining tablespoon of butter and increase the heat. Toss in the sliced yellow onion and sauté for 4-5 minutes until soft and semi-translucent.

Divide the 2 lbs of ground beef into four equal portions, seasoning each with salt, garlic powder, and pepper. Sear for about 2 minutes on one side, then flip and flatten with a spatula, cooking for a total of 7-8 minutes.

Chop the cooked ground beef and sautéed onions together in the skillet. Place two slices of American cheese on top of each portion and cover for about 1-2 minutes to melt the cheese.

Spread mayonnaise on the toasted hoagie rolls, fill each with the cheesy beef and onion mixture, and add sliced tomatoes and shredded lettuce.