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 vertically, then place them in a mixing bowl.
Toss the sprouts with half of the olive oil, half of the sea salt, and half of the black pepper until evenly coated.
Spread the sprouts on the baking sheet in a single layer and roast for 20 to 25 minutes until the outer leaves are caramelized and crispy.
While the sprouts roast, season the chicken breast on both sides with garlic powder, rosemary, and the remaining salt and pepper.
Heat the remaining olive oil in a skillet over medium-high heat and sear the chicken for 6 to 7 minutes per side until the internal temperature reaches 165°F.
In a small saucepan over low heat, whisk together the balsamic vinegar and maple syrup, simmering for 3 to 5 minutes until it thickens into a glossy glaze.
Slice the chicken and serve alongside the roasted sprouts, drizzling the warm balsamic glaze over the entire dish before serving.