Preheat oven to 200C/400F/Gas 6.
Spray a large frying pan with cooking spray and add the onions, carrots, and garlic. Cook over medium heat for a few minutes then add a mugful of water. Cook for 10 minutes or until everything has softened. Add extra water if needed.
Meanwhile, break the spaghetti in half and cook according to the package instructions. Drain well and return to the pan.
Place the tomato purée, Italian herbs, 1 teaspoon of rosemary, passata, and balsamic vinegar into the vegetable mixture. Stir and bring to the boil. Reduce heat to simmer for 5 minutes.
Add the tomato mixture to the pan of spaghetti along with the diced tomatoes. Stir to combine.
Transfer the spaghetti and sauce to a large baking dish.
Spray the chicken breasts with cooking spray. Sprinkle with the parmesan, the other 2 teaspoons of dried rosemary, and season with salt and pepper.
Place on top of the spaghetti and bake for 15-20 minutes or until chicken is cooked through.
Serve 1 chicken breast per person with spaghetti and salad.