Mix the sauce: In a small bowl, combine brown sugar, Dijon mustard, apple cider vinegar, cinnamon, and nutmeg.
Add sauce: Pour the sauce over the ingredients in the slow cooker and stir to coat.
Cook: Cover and cook on low for 3-4 hours or high for 1.5-2 hours, or until apples are tender and kielbasa is heated through.
Serve: Stir gently and serve hot. Enjoy on their own or with toothpicks.
