01 - Heat olive oil in a large skillet over medium-high heat. Add the ground beef and chopped onion, breaking up the meat with a spatula. Cook until the beef is browned and cooked through, approximately 6 to 7 minutes. Season with salt and pepper to taste.
02 - Drain any excess fat from the skillet if necessary. Stir in the ketchup and mustard, mixing until well combined and heated through.
03 - Lay the tortillas flat on a clean work surface. Place one slice of cheddar cheese in the center of each tortilla. Divide the beef mixture evenly among the four tortillas, then top each with shredded lettuce, diced tomato, and pickle slices.
04 - Drizzle mayonnaise over the filling on each tortilla. Fold in the sides, then roll up tightly from the bottom to fully enclose the filling.
05 - For a crispy exterior, wipe the skillet clean and return to medium heat. Place each wrap seam-side down in the skillet and grill for 1 to 2 minutes per side until golden and crisp.
06 - Slice each wrap in half diagonally and serve immediately while warm.