Preheat oven to 400°F and line a baking sheet with tin foil or a silicone baking mat.
In a medium bowl, mix the potatoes, olive oil, rosemary, salt and pepper together. Place the coated potatoes on the baking sheet and bake for 10 minutes.
While the potatoes cook, prepare the chicken marinade. In a small bowl, mix together the dijon mustard, soy sauce, garlic, maple syrup, rosemary and pepper. Set this aside.
In the bowl you used for the potatoes, add the chopped broccoli and bell pepper and season with the olive oil, garlic powder, salt and pepper. Mix together.
Once the potatoes have cooked for 10 minutes, remove the baking tray from the oven and push the potatoes to one side to make room for the remaining ingredients. Add the raw chicken breasts and uncooked vegetables to the tray and drizzle the marinade over the chicken. Bake for another 20 minutes or until the chicken is cooked through.
For extra tastiness, pair with a dollop of tzatziki. Enjoy!