In a small bowl, mix mayonnaise, ketchup, mustard, and pickle relish to make the sauce. Set aside.
Divide the ground beef into 4 equal balls and season with salt, black pepper, and garlic powder (if using).
Place one tortilla on a flat surface and press one beef ball thinly across the tortilla.
Heat a skillet over medium-high heat and place the tortilla beef-side down into the pan.
Cook for 2–3 minutes until the beef is browned and crispy.
Flip the tortilla so the beef faces up, then sprinkle cheese evenly over the beef.
Add pickles or onions if using, then fold the tortilla in half.
Cook for 1–2 minutes per side until golden and crispy and the cheese is melted.
Repeat with remaining tortillas. Slice into wedges and serve with sauce for dipping.