Heat vegetable oil in a 12-inch skillet over medium heat.
Place the flour tortilla in the skillet. Layer half of the Swiss cheese on one half of the tortilla, followed by the corned beef, sauerkraut, and the remaining Swiss cheese.
Fold the tortilla in half. Cook until golden brown on one side, approximately 4 to 5 minutes.
Flip the quesadilla to the other side and cook until golden brown, another 4 to 5 minutes.
Remove the quesadilla from the pan and cut it into 4 wedges.
Serve with Russian dressing on the side.
Notes
For a crispier quesadilla, you can brush the outside of the tortilla with a little extra oil before cooking.