Slice duck into fajita size pieces and place in a container. Add in liquid smoke, fajita seasoning, and any other wanted seasoning. Cover and let sit in fridge for 6 hours.

Remove duck from fridge and pour into a medium skillet and cook on medium heat for about 10-12 minutes.

Slice up onions, bell pepper, and mushrooms. Sauté in a medium skillet with 2 tablespoons of butter. Serve with duck on tortilla with sour cream, cheese, lettuce, and any other wanted condiment.