Divide the ground beef into 8 equal portions and roll them into balls.

In a small bowl, combine mayonnaise, ketchup, and sriracha (if using) to make the special sauce; set aside.

Heat a large griddle or cast-iron skillet over medium-high heat until very hot.

Place a beef ball onto a tortilla and smash it flat onto the hot griddle with a spatula, cooking for 2-3 minutes until browned.

Flip the burger-tortilla, immediately add a half slice of cheese, and cook for another 1-2 minutes until the cheese is melted and the tortilla is slightly crispy.

Remove from the griddle and repeat with the remaining beef balls and tortillas.

Assemble each smash burger taco by adding shredded lettuce, diced tomatoes, diced pickles, and diced onion.

Drizzle with the prepared special sauce and serve immediately.