Begin by gathering all necessary ingredients.

Flatten each slice of bread using a rolling pin until completely smooth. Trim the crusts to create 4x4-inch squares, and spread a thin layer of yellow mustard evenly over each slice (approximately 3/4 teaspoon per slice).

For assembly, take one slice of bread and place a halved cheese slice at the edge closest to you, followed by a hot dog positioned horizontally on top. If required, trim the hot dog ends so they do not extend beyond the bread edges. Next, spoon about 1 1/2 teaspoons of minced onion over the cheese slice, then add 1 teaspoon of sweet pickle relish.

Carefully roll the bread tightly around the filling, applying gentle pressure to seal the edges. Cut each roll into three equal pieces, roughly 1 1/4 inches in size, and arrange them on a serving platter. Repeat the process for the remaining ingredients. Preheat an air fryer to 400 degrees F (200 degrees C) for 5 minutes or according to the manufacturer's instructions. Lightly spray the tops and sides of the roll-ups with cooking spray. In two batches, place the roll-ups in the basket, ensuring they are spaced 1/2-inch apart, and cook until the bread is lightly golden brown, about 5 minutes.

In a small bowl, combine the barbecue sauce, mayonnaise, and seasoned salt, mixing until well blended.

Serve the hotdog roll-ups alongside the mayonnaise mixture for dipping.