01 - Heat olive oil in a large skillet over medium-high heat. Add the ground beef and chopped onion, breaking the meat apart with a spatula. Cook until evenly browned and no longer pink, approximately 6 to 7 minutes. Season with salt and pepper to taste.
02 - Drain any excess fat from the skillet. Stir in the ketchup and mustard, mixing thoroughly until the sauce coats the beef evenly and everything is heated through.
03 - Lay the tortillas flat on a clean surface. Place one slice of cheddar cheese in the center of each tortilla. Divide the seasoned beef mixture evenly among the four wraps, layering it over the cheese. Top each with shredded lettuce, diced tomato, and pickle slices.
04 - Drizzle mayonnaise evenly over the top of each assembled wrap.
05 - Fold in the left and right sides of each tortilla toward the center, then roll tightly from the bottom edge upward to fully enclose the filling.
06 - Wipe the skillet clean and return it to medium heat. Place each wrap seam-side down in the skillet and grill for 1 to 2 minutes per side until the exterior is golden and lightly crisp.
07 - Slice each wrap in half diagonally and serve immediately while warm.