Prep: Preheat your oven to 375°F (190°C). Line a small baking dish with parchment paper or grease it lightly to make cleanup easier (the sugar gets very sticky!).
Whisk: In a medium bowl, whisk together the brown sugar, ketchup, Dijon, soy sauce, vinegar, garlic powder, and pepper until the sugar begins to dissolve and the mixture is smooth.
Coat: Add the kielbasa rounds to the bowl. Toss thoroughly to ensure every slice is fully submerged in the glaze.
Arrange: Spread the sausage in a single layer in the baking dish. Pour any extra glaze from the bowl over the top.
Bake: Bake for 20–25 minutes. Important: Stir the pieces halfway through the cooking time to ensure the glaze caramelizes evenly on all sides.
Rest & Serve: Let the bites cool for about 5 minutes; this allows the glaze to "set" and become extra tacky. Transfer to a platter, add toothpicks, and garnish with parsley.