1Cut up a pound of Kielbasa sausage and place it in the slow cooker.
2Dice two Granny Smith apples and add them to the slow cooker.
3In a mixing bowl, combine 1/2 cup brown sugar, 1/2 cup apple cider, 2 tablespoons Dijon mustard, 1 teaspoon garlic powder, 1 teaspoon salt, 1 teaspoon pepper, and 1 teaspoon red pepper flakes.
4Whisk all ingredients until combined and then pour the mixture over the apples and sausage in the slow cooker.
5Give everything a good stir to ensure it's coated, then place the lid on the slow cooker.
6Set the temperature to low for 3-4 hours and let it cook.
7Once the time is up, remove the lid, give it another quick stir, and serve.