1. On a work surface, cover half of the tortilla with the onion confit. Top with 1 slice of cheese, cutting it to fit as needed. Cover with the chicken, arugula and remaining slice of cheese. Fold the tortilla in half over the fillings.
2. In a large skillet over medium heat, brown the quesadilla in the oil for 2 to 3 minutes on each side. Cut in half, if desired. Serve with Dijon mustard, sour gherkins and arugula salad, if desired. Serve immediately.

NOTE FROM RICARDO

The cooked chicken can be replaced with anything you happen to have on hand: ham, thinly sliced cooked sausage, duck confit or braised meat. The same goes for the arugula: replace it with spinach or fresh herbs.