Preheat and Prepare: First things first, preheat your oven to 200°C (180°C fan). Season both sides of the chicken breasts generously with salt and pepper.

Sear the Chicken: Heat the olive oil in a large, oven-safe frying pan or skillet over a medium-high heat. Add the chicken breasts and sear for 3-4 minutes on each side until they are beautifully golden brown. They don't need to be cooked through at this stage. Once seared, remove them from the pan and set aside on a plate.

Sauté the Aromatics: Lower the heat to medium and add the chopped onion to the same pan. Cook for about 5 minutes, stirring occasionally, until it has softened. Add the minced garlic and dried oregano and cook for another minute until fragrant.

Build the Sauce: Pour in the chopped tomatoes and balsamic vinegar. Add the halved cherry tomatoes and the optional sugar. Give everything a good stir, scraping up any browned bits from the bottom of the pan – this is where so much flavour lives! Season with salt and pepper.

Simmer Briefly: Bring the sauce to a gentle simmer and let it cook for 5 minutes to allow the flavours to meld together. What works best for me is using the back of a spoon to gently crush some of the cherry tomatoes to release their juices into the sauce.

Return the Chicken: Nestle the seared chicken breasts back into the pan, spooning some of the sauce over them.

Add the Toppings: Scatter the torn fresh basil leaves over the sauce. Arrange the torn or sliced mozzarella evenly over the top of the chicken breasts.

Bake to Perfection: Transfer the entire pan to the preheated oven. Bake for 15-20 minutes, or until the chicken is cooked through and the cheese is melted, bubbling, and starting to turn golden brown in spots.

Rest and Serve: Carefully remove the pan from the oven and let it rest for 5 minutes before serving. This allows the juices in the chicken to redistribute, ensuring it's extra tender. Garnish with a few more fresh basil leaves if you like.