Preheat oven to 425°F. Spray baking sheet with cooking spray or brush with extra olive oil.
Toss the broccoli, carrots and onion in a large bowl with the olive oil, ½ teaspoon of salt and ¼ teaspoon pepper. Spread on baking sheet and roast for 15 minutes.
Place the chicken on a platter and sprinkle with ½ teaspoon of salt and ¼ teaspoon of pepper. Let it come to room temperature while the vegetables are roasting.
Prepare the glaze by combining the honey, balsamic vinegar, butter and garlic powder in a microwave safe bowl. Microwave for 30 second intervals until it's dark and bubbly and slightly clings to the spoon. You can also heat it up in a pan on the stove. Keep 2 tablespoons of it reserved to brush on the chicken and the rest will be for serving.
Remove the pan from the oven and give the vegetables a quick stir. Add the tomatoes and chicken to the pan and brush the chicken with the glaze. Roast for 20-25 minutes or until chicken reaches 165°F.
Serve with extra glaze.
The broccoli becomes nice and charred in this recipe, if you want your broccoli with less char, add it at the same time you add the chicken and tomatoes, drizzling it with a little olive oil and salt and pepper.A little sriracha sauce added to the glaze gives it a little kick.