Prepare the Special Sauce: In a small bowl, combine mayonnaise, ketchup, dill pickle relish, yellow mustard, white vinegar, and sugar. Whisk well until all ingredients are thoroughly combined and the sauce is smooth. Taste and adjust seasonings if needed. Cover and refrigerate until ready to use to allow flavors to meld.

Prepare the Beef Patties: In a medium bowl, gently break up the ground beef. Add salt, black pepper, garlic powder, and paprika. Mix lightly with your hands until just combined, being careful not to overmix, which can make the burgers tough. Divide the seasoned beef into 8 equal portions (about 2 oz each) and loosely form them into balls.

Heat Skillet or Griddle: Heat a large cast-iron skillet or flat-top griddle over medium-high heat until very hot, about 3-5 minutes. A hot surface is crucial for a good 'smash' and crispy crust.

Smash and Cook the Beef onto Tortillas: Place a beef ball onto the hot skillet. Immediately place a flour tortilla on top of the beef ball. Using a sturdy spatula or a burger press, firmly smash the beef ball down into a thin patty, pressing it directly onto the tortilla. Cook for 1-2 minutes until the beef is deeply browned and crispy on the edges.

Flip and Add Cheese: Carefully flip the beef-tortilla combination so the tortilla side is now down on the skillet and the cooked beef is facing up. Immediately place a slice of American cheese on top of the hot beef patty. Continue to cook for another 30-60 seconds, or until the cheese is melted and bubbly and the tortilla is lightly golden and slightly crispy.

Assemble the Tacos: Transfer the cooked smashburger tacos to a plate. Top each taco with a generous spoonful of the prepared special sauce, a few slices of dill pickle, and a sprinkle of finely diced yellow onion if desired. Serve immediately while hot.