Preheat oven to 400°F and line a large baking sheet with parchment paper.
Trim and halve the Brussels sprouts, and cut the chicken breast into bite-sized 1-inch pieces.
In a large bowl, whisk together the olive oil, 1 tablespoon of balsamic vinegar, honey, salt, pepper, and garlic powder.
Add the chicken and sprouts to the bowl, tossing thoroughly until every piece is evenly coated in the marinade.
Spread the mixture in a single layer on the baking sheet, ensuring enough space for the sprouts to crisp up.
Roast for 20-25 minutes, tossing halfway through, until the chicken is cooked through and the sprouts are charred.
Drizzle the remaining tablespoon of balsamic vinegar over the hot pan before serving for an extra punch of flavor.