In a large skillet, heat the vegetable oil over medium-high heat.
Divide the ground beef into 8 equal portions and form them into loose balls. Season each ball with kosher salt and black pepper.
Once the oil is hot, place the beef balls in the skillet and smash them down with a spatula to form thin patties.
Cook for about 3-4 minutes until the edges are crispy, then flip and cook for an additional 2-3 minutes. Remove the patties from the skillet and let them rest.
In the same skillet, lightly spray the corn tortillas with cooking spray and warm them for about 30 seconds on each side until pliable.
In a small bowl, mix together the mayonnaise, ketchup, mustard, white vinegar, and diced onions to create the special sauce.
To assemble the tacos, place a warm tortilla on a plate, add a smashed burger patty, and top with shredded lettuce, diced tomatoes, cheddar cheese, pickles, and a drizzle of the special sauce.
Repeat with the remaining tortillas and ingredients.
Serve immediately while warm.