Combine all the special sauce ingredients in a small bowl and set aside.

Heat a large frying pan or griddle over medium-high heat.

Divide the ground beef into two portions and place each of them on a tortilla. Use your hands to press and spread the ground beef over the tortilla.

Season each smash burger with herbed salt and pepper.

Squeeze a little optional mustard around each smash burger if using the mustard option.

Place one smash burger, ground beef side down, in the pan or griddle. Cook for two to four minutes or until the beef is browned and done.

Using a large spatula turner, carefully flip the burger tortilla over.

Add optional diced onions and sliced cheese to the tortilla burger, and let it cook for another minute until the cheese melts.

Once the cheese melts, add shredded lettuce and drizzle with the special sauce. Repeat.

Fold the burger tortilla in half like a taco and place it on a plate. Serve whole or cut the taco in half and serve immediately.