Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper for easy cleanup.
Trim the ends off the Brussels sprouts and slice them in half lengthwise, then cut the chicken breast into even 1-inch pieces.
Place the sprouts and chicken on the baking sheet, drizzling with olive oil and sprinkling with sea salt, black pepper, and garlic powder.
Toss everything thoroughly to coat and spread into a single layer, ensuring the sprouts are cut-side down for maximum caramelization.
Roast for 20 to 25 minutes until the chicken is cooked through and the sprouts are beautifully charred and tender.
While roasting, simmer the balsamic vinegar and honey in a small saucepan over medium-low heat for 5 minutes until it thickens into a glossy glaze.
Transfer the roasted mixture to a bowl, drizzle with the warm balsamic glaze, and garnish with chopped walnuts for a delightful crunch.