Make the sauce. Whisk together all special sauce ingredients in a small bowl. Refrigerate until ready to use.
Prep the beef. Divide ground beef into 8 equal balls (about 2 oz each). Season generously with salt and pepper.
Heat your skillet. Place a cast iron skillet or griddle over high heat. Let it get screaming hot — about 2 minutes.
Smash those patties. Place a tortilla flat in the skillet. Add a beef ball to the center, then use a heavy spatula or burger press to smash it firmly into the tortilla. Press hard and hold for 5 seconds.
Cook the first side. Cook for 2–3 minutes until the edges are crispy and brown.
Add cheese and flip. Place a slice of American cheese on top, then flip the taco. Cook another 1–2 minutes until the tortilla crisps up.
Assemble. Transfer to a plate, beef-side up. Top with special sauce, shredded lettuce, pickles, and diced onion. Serve immediately.