Preheat your oven to 200℃. Slice your onion
Make 4 slits through your chicken breast and then share the pesto between those 4 slits. Season the chicken with salt and pepper and place into an oven dish.
In a pan spray 10 squirts of oil then add your sliced onion, cook this on a high heat for 2-3 mins, stirring regularly, until they colour then turn the heat to low and add your tinned tomatoes and 4 leaves of fresh basil (1 teaspoon dried basil),
Simmer this for 2-3 minutes, stirring careful so the sauce does not catch and burn and then carefully spoon it around the chicken in the oven proof dish.
Put your mozzarella on top of the chicken (I popped some paprika on as well in order to give some colour
Tightly cover with silver foil and place in the oven for 20 mins. Then remove the foil and put back in the oven uncovered for a further 10 minutes.
Remove from the oven, transfer your chicken to a plate, stir the sauce so that it incorporates the chicken juices, then spoon THAT on your plate and bobs your uncle!