In a small bowl, mix together Greek yogurt, ketchup, Dijon mustard, dried onion, dill pickle relish, garlic powder, and salt. Set aside.
In a skillet over medium-high heat, cook the seasoned beef with the diced onions and seasoned salt until the beef is no longer pink and the onions are translucent. Drain any excess fat.
Lay out the flour tortillas. On one half of each tortilla, place half a slice of American cheese
Next, add an even layer of the cooked beef and onions. Drizzle some of the Big Mac sauce directly on top of the beef.
Add another slice of American cheese on top of the sauce. Fold the tortilla over to create a half-moon shape.
Heat a non-stick skillet over medium heat. Spray with non-stick cooking spray. Place the quesadilla in the skillet, cooking until the tortilla is golden brown and crispy on one side, then flip and cook the other side until the cheese is melted and the tortilla is golden brown.
Once cooked, open the top half of the quesadilla slightly and add shredded lettuce and sliced pickles. Alternatively, you can serve them on top.
Cut each quesadilla into slices and serve immediately with the remaining Big Mac sauce for dipping.