Add the ground beef, onion, 1 tsp salt, and 1/4 tsp pepper to a skillet over medium heat. Cook, while breaking up the beef, until the beef is browned, about 10 minutes.
Drain the beef in a colander and set aside.
Heat a griddle over medium to medium-high heat or about 350°F.
Lay the tortillas out flat then cover half of each tortilla evenly with all the beef mixture.
Sprinkle the cheese evenly onto the beef mixture then sprinkle on the diced pickles.
Fold the tortillas in half to cover the filling then press them down with your hands.
Brush the tops of the quesadillas with a little oil then place them oiled side down onto the griddle and brush the other side with a little olive oil.
Cook until browned then flip until browned on the other side, about 2 minutes per side.
Mix together the mayonnaise and Dijon mustard in a bowl and serve with the quesadillas.