Preheat oven to 400°F and line a large baking sheet with parchment paper.
Trim the ends of the Brussels sprouts and cut them in half, then cut the chicken breast into 1-inch bite-sized pieces.
Place the chicken and sprouts on the baking sheet, drizzle with olive oil, and sprinkle with garlic powder, sea salt, and black pepper.
Toss well to coat and spread in a single layer, ensuring the sprouts are cut-side down for maximum caramelization.
Roast for 20 to 25 minutes, or until the chicken is cooked through and the sprouts are tender with charred edges.
While roasting, place the walnuts in a small dry skillet over medium heat for 3 to 5 minutes until fragrant and toasted.
In a small bowl, whisk together the balsamic vinegar and honey until smooth.
Remove the tray from the oven, drizzle the balsamic mixture over the chicken and sprouts, add the toasted walnuts, and toss to glaze before serving.