Preheat your oven to 400°F (200°C) and line a large rimmed baking sheet with parchment paper for easy cleanup.
Trim the woody ends off the Brussels sprouts and slice them in half; cut the chicken breast into uniform 1-inch cubes.
Place the chicken and sprouts on the baking sheet, then drizzle with the olive oil and sprinkle with sea salt, black pepper, and garlic powder.
Toss everything thoroughly with your hands or tongs to ensure an even coating, then spread the mixture out into a single layer.
Roast in the center of the oven for 20 to 22 minutes, or until the chicken is cooked through and the sprouts have developed crispy, caramelized edges.
While the tray is in the oven, whisk together the balsamic glaze and honey in a small bowl until smooth.
Remove the sheet pan from the oven, drizzle the balsamic-honey mixture over the hot food, and toss gently to coat.
Top with the chopped walnuts and serve immediately while the glaze is warm and glossy.