In a medium mixing bowl, knead the ground beef with the salt and form into 8 even balls.
Lay the tortillas on a work surface and press the ground beef onto the top of each tortilla, patting down evenly and filling it out to the edges of the tortilla.
Air Fry in batches at 385°F / 195°C for 4 Minutes. After 4 Minutes, add one slice of American cheese to the top of each tortilla. Air Fry for an additional 1-2 Minutes, or until the cheese has melted.
While the tortillas are air frying, prepare the sauce. In a small bowl, whisk together the ketchup, mayonnaise, and yellow mustard. Set aside.
Top each smash burger taco with diced tomato, diced onion, shredded lettuce, and a good drizzle of sauce. Serve with extra sauce on the side.