Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Trim the stem ends of the Brussels sprouts and slice each one in half vertically.
Slice the smoked chicken sausage into 1/2-inch thick rounds.
Place the Brussels sprouts and sausage rounds onto the prepared baking sheet.
Drizzle with avocado oil and sprinkle with sea salt, black pepper, and garlic powder.
Toss everything together with your hands or a spatula until evenly coated, then spread into a single layer.
Turn the Brussels sprouts so they are mostly cut-side down to ensure they get a deep, golden char.
Roast for 20 to 25 minutes, tossing halfway through, until the sprouts are tender and the sausage is browned.
Remove from the oven and immediately drizzle with the balsamic vinegar while still hot.
Toss one final time to distribute the vinegar and serve immediately.