For BBQ Duck: Season duck legs and place in pot with sauce and water. Make sure that the liquid covers the duck legs, if not add more water and barbecue sauce. Simmer for 3 hours, until meat falls easily from the bone. Remove the meat from liquid and continue boiling until it is reduced to a thick sauce. Let meat cool and carefully remove bones and cartilage. Stir into sauce and take off the heat.
For Mango-Avocado Salsa: Combine all ingredients in a bowl and season to taste.
For Quesadilla: Heat oven to 500 degrees. Place 4 tortillas on a flat work surface. Sprinkle 1/2 tablespoon each of chopped red onions and jalapeños over each tortilla.
Divide cheese and into 8 portions and duck into four portions. Spread one portion of duck and of cheese over each tortilla. Season lightly with salt and pepper. Cover each quesadilla with another tortilla and repeat the same procedure with onions, chiles, and cheese, minus the duck. Cover with the remaining four tortillas.
Lightly oil the top tortilla with olive oil and dust lightly with the ancho powder. Bake in oven for 5 – 10 minutes, until top tortilla is crispy, but not burned. Divide hot quesadillas into wedges and serve with mango-avocado salsa.