Preheat oven to 400°F and spray a large baking sheet/tray with cooking spray or line with parchment paper
To make the marinade, combine the balsamic vinegar, honey, 1 tablespoon olive oil, garlic, salt, black pepper and herbs in a small bowl. Set aside.
In another bowl, mix the sweet potato cubes with the remaining 1 tablespoon of olive oil. Transfer to the prepared baking tray and roast at 400°F for 15 minutes. Remove from the oven and transfer to a large bowl.
Add chicken, onion, broccolini and tomatoes to the bowl with the potatoes. Pour ⅔ of the prepared marinade over them and toss to coat.
Transfer the mix back onto the baking tray and roast in the oven at 400°F for another 15 minutes until chicken is cooked through (no longer pink). Baste with more marinade frequently as required. Remove from oven and enjoy!