In a small bowl, whisk together the mayonnaise, ketchup, Dijon mustard, white vinegar, paprika, and garlic powder until smooth. Season to taste with salt. Cover and refrigerate.
Make The Smash Burgers:
Lay the tortillas flat on a clean work surface. Spread half the ground beef over each, pressing it into a thin layer with your hands or a fork and leaving a small border all around the edge. Season each patty to taste with salt and pepper.
Heat the olive oil in a large skillet over medium-high heat. Place one tortilla meat-side down in the skillet. Smash it down lightly with a spatula to ensure good contact with the hot surface. Cook for 2-3 minutes, until the beef is browned and crisp.
Flip the tortilla and immediately top with 1 cheese slice. Cover to help the cheese melt. Cook for 30 seconds to 1 minute more. Transfer to a wire rack in a low oven to keep warm.
Repeat with the remaining tortilla and beef.
Assemble And Serve The Tacos:
Top each smash burger taco with half the shredded lettuce, half the onions, and half the pickles, Drizzle each with Big Mac sauce and serve immediately.