Marinate the chicken: In a small bowl, whisk together the balsamic vinegar, olive oil, garlic powder, dried rosemary, salt, and pepper. Place the chicken breasts in a resealable bag and pour the marinade over them. Refrigerate for at least 30 minutes, or overnight for best results.
Prepare the vegetables: Preheat the oven to 400°F (200°C). Toss the carrots, Brussels sprouts, and red onion with olive oil, salt, and pepper. Spread them out in an even layer on a sheet pan.
Add the chicken: Remove the marinated chicken from the bag and place it on the sheet pan with the vegetables.
Bake: Roast for 25-30 minutes, or until the chicken is fully cooked and the vegetables are tender and caramelized.
Serve: Let the chicken rest for a few minutes before slicing. Serve with the roasted vegetables and any remaining balsamic glaze.
This makes 4 servings. Each serving is 3 WW Points. Enjoy!