Make the tomato sauce first by heating a tbsp. of olive oil in a medium sized saucepan over a medium to high heat.
Add the onion and sweat until soft and starting to colour slightly, about 5 to 7 minutes then add the garlic and oregano and fry for a further minute.
Add the chopped tomatoes then reduce the heat and simmer for 10 minutes.
While the sauce is simmering, heat a frying pan over a medium to high heat, add the remaining olive oil. Season the chicken breasts then fry for about 5 minutes on each side and a nice golden brown.
Place the seared chicken into an oven proof dish and place the mozzarella over each chicken breast.
Add the balsamic vinegar and sugar to the tomato sauce, stir and season to your liking.
Spoon the tomato sauce evenly over the chicken and then sprinkle the breadcrumbs and parmesan evenly over each chicken breast. Add a sprinkle of extra oregano if you wish.
Bake for a further 10 minutes until the chicken is cooked through.
Serve with a nice green salad and some herb roasted new potatoes.