Place the chicken into a shallow dish and marinate with 2 tbsp of olive oil, the garlic, oregano, chilli and season with salt and pepper. Toss well to combine then set aside at room temp while you cook the onions or in the fridge if you want to marinate for longer.
Peel the onions, cut in half lengthways and thinly slice them with the grain - from root end to tip. This is important for achieving silky caramelised onions.
Place the remaining olive oil, onions, and a good pinch of salt in a medium, heavy based saucepan. Stir together then cover with a lid and place this over a medium/high heat to cook for 3 minutes, until the onions sweat and begin to release their juices and drop.
Stir the onions then replace the lid, turn the heat down to a medium and cook for another 3 minutes before removing the lid, stirring, and cooking over a low heat uncovered for 15 minutes, stiring often, to really begin to caramelise. During this time, make sure you stir through any bits that caramelise and stick to the pan. Add the balsamic vinegar to the onions and continue to cook for 5 minutes, continuing to stir, to evaporate the liquid until slightly thickened.
Transfer the onions to the bottom of a baking dish and place the marinated chicken on top. Toss the tomatoes in 1 tbsp of olive oil, the remaining balsamic and a little salt and pepper then scatter this over and around the chicken.
Roast in the preheated oven for 15 minutes then spoon some of the onions and tomatoes over the chicken and scatter the cheese over each breast. Return to the oven for 5 minutes to melt and caramelise the cheese.
Serve scattered with basil leaves and a preferred side of rice or mash potato and a simple mixed leaf salad.
Servings 0