Prepare the Beef: In a bowl, combine the ground beef, Worcestershire sauce, garlic powder, onion powder, salt, and pepper. Mix gently to combine, being careful not to overwork the meat.

Form the Patties: Divide the ground beef mixture into 4 equal portions. Roll each portion into a ball.

Smash the Patties: Heat a large cast iron skillet or griddle over medium-high heat. Add a small amount of oil or butter. Place a beef ball onto the hot surface and immediately smash it down with a spatula or burger press until it's very thin (about 1/4 inch). Repeat with the remaining beef balls, being careful not to overcrowd the pan.

Cook the Patties: Cook the smashed patties for 2-3 minutes per side, or until they are browned and crispy around the edges and cooked through. As the patties cook, they will release some fat. Drain off any excess fat from the skillet.

Assemble the Quesadillas: Lay one tortilla flat on a clean surface. Sprinkle half of the shredded cheese evenly over the tortilla. Top with one cooked smashburger patty, 1/4 of the diced onion (if using), and a few pickle slices (if using). Drizzle with Smashburger Sauce. Sprinkle with the remaining cheese. Top with the second tortilla.

Cook the Quesadillas: Heat a clean skillet or griddle over medium heat. Add the assembled quesadilla to the hot skillet. Cook for 3-4 minutes per side, or until the tortilla is golden brown and the cheese is melted and gooey. Repeat with the remaining tortillas and filling.

Serve: Cut each quesadilla into wedges and serve immediately.

Smashburger Sauce: In a small bowl, combine the mayonnaise, ketchup, yellow mustard, sweet pickle relish, garlic powder, and paprika. Mix well.