Divide the Beef: Divide the ground beef into 6 equal portions, roughly 2.3 ounces each, so each tortilla gets an even layer.
Spread and Season: Place each portion on a tortilla and spread it into a thin, even layer covering most of the surface, then season generously with salt and black pepper.
Sear the Beef: Place each tortilla beef-side down in a hot skillet over medium-high heat and cook for 4-5 minutes until the beef is deeply browned and cooked through, creating a caramelized crust.
Add the Cheese: Flip each tortilla so the beef faces up, then immediately top with 3 slices of cheddar cheese on the cooked beef side.
Melt the Cheese: Cover the skillet with a lid and cook for 1-2 minutes until the cheddar is fully melted and gooey.
Make the Sauce: While the cheese melts, stir together 3 tablespoons mayonnaise, 2 tablespoons BBQ sauce, 1 tablespoon mustard, and 3 tablespoons finely diced pickles in a small bowl.
Build Your Taco: Transfer each tortilla to a plate, spread the sauce over the melted cheese, add lettuce and tomato slices, then sprinkle with diced red onion and fold the tortilla in half.