To prepare the duck, combine olive oil, honey, Dijon, salt and pepper. Slather on duck. Let stand in fridge for at least 30 minutes. Preheat oven to 400°. Place the duck in a baking dish in the hot oven for 15-17 minutes (If you like your duck a little more rare, take it out after 12-14 minutes). Let the duck cool and slice into thin strips.
To prepare the cheese filling, combine yogurt, Fontina, salt and pepper to taste, and cayenne. Set aside (You will also use some of this mixture for a garnish).
To prepare the plums, combine the plums with olive oil, vinegar and salt and pepper to taste. Arrange the plums on a baking dish and bake for 10-15 minutes.
When you ready to assemble your quesadillas, place tortillas down on a clean work space. Spread cheese mixture on one half of tortilla. Top with plums and then with duck. Fold over empty side of tortilla to create a half moon shape.
Reduce temp of oven to 350°. Arrange tortillas on a baking sheet and bake for 10-15 minutes or until edges start to brown. Garnish with dollop of cheese filling mixture.