01 -
Heat a large skillet over medium-high heat until hot.
02 -
Add ground beef to the skillet, season with kosher salt and pepper, and cook, breaking it into small pieces, until browned and cooked through, about 6–8 minutes.
03 -
Stir in finely chopped onion and cook until softened and translucent, approximately 2–3 minutes.
04 -
Arrange American cheese slices over the beef mixture, allow them to melt, then gently stir to incorporate the cheese thoroughly with the meat.
05 -
Divide the cheesy beef mixture evenly among the split sub rolls or sandwich buns.
06 -
Top each sandwich with shredded lettuce, diced tomato, and pickles if desired.
07 -
Drizzle ketchup and/or mayonnaise over the filling to taste.
08 -
Close each sandwich and serve immediately while hot.