Preheat your oven to 400°F (200°C) and line a large baking sheet with parchment paper.
Trim the ends of the Brussels sprouts and slice them in half, then cut the chicken breast into bite-sized cubes.
Place the chicken and Brussels sprouts on the baking sheet, drizzle with olive oil, and sprinkle with sea salt, black pepper, and garlic powder.
Toss everything together until evenly coated and spread in a single layer to ensure even roasting.
Roast for 20-25 minutes, or until the chicken is cooked through and the Brussels sprouts are tender with browned, crispy edges.
While the tray is roasting, lightly toast the walnuts in a dry skillet over medium heat for 3-5 minutes until fragrant.
Remove the tray from the oven, drizzle the balsamic glaze over the chicken and sprouts, and toss to combine.
Transfer to a plate and top with the toasted walnuts before serving.