Preheat your oven to 400°F and line a large rimmed baking sheet with parchment paper.
Trim the ends off the Brussels sprouts and slice each one in half vertically.
Cut the chicken breast into uniform 1-inch cubes to ensure even cooking.
In a large mixing bowl, combine the Brussels sprouts and chicken cubes with olive oil, sea salt, black pepper, and garlic powder.
Toss the mixture thoroughly until every piece is well-coated in oil and seasoning.
Spread the chicken and sprouts in a single layer on the prepared baking sheet, ensuring they are not overcrowded so they roast rather than steam.
Roast for 20 to 25 minutes, tossing the ingredients halfway through, until the chicken is cooked through and the sprouts are deeply browned.
While the tray is in the oven, whisk the balsamic vinegar and honey in a small saucepan over medium-low heat for 3 to 5 minutes until it thickens into a glaze.
Remove the tray from the oven and immediately drizzle the warm balsamic glaze over the chicken and sprouts before serving.