You LUCKY devil you!!!! I'd almost kill for leftover duck breast - lol!!! Have so many Asian cookbooks with recipes for duck stirfries, yet never have any leftover roast duck to try them, & the parts bought separately are so expensive.
Here's a recipe that I'd like to try from The Food and Cooking of Thailand:
9 oz. wild duck meat
1 tbsp. sesame oil
1 tbsp. vegetable oil
4 garlic cloves, finely sliced
1/2 tsp. dried chili flakes
1 tbsp. fish sauce
1 tbsp. soy sauce
1/2 cup water
1 head broccoli, cut into small florets
coriander & 1 tbsp. toasted sesame seeds to garnish
(Variations: Bok choy or Chinese flowering cabbage can be used instead of broccoli.)
Cut the duck meat into bitesize pieces. Heat the oils in a wok or large heavy frying pan & stirfry the garlic over a medium heat until golden but not burnt. Add the duck & stirfry for a further 2 minutes (I'm assuming this is for raw duck meat). Stir in the chili flakes, fish sauce, soy sauce, & water. Add the broccoli & continue to stirfry for about 2 minutes or until just cooked through. Serve on warmed plates garnished with coriander & sesame seeds.
Obviously, since your leftover duck is already cooked, the stirfry time would be less. I also would not add the garlic first - it burns way too fast. I'd add it at the same time you add the duck.