Cut into the chicken breasts to make slices, being careful not to cut all the way through. You want 5 incisions in each breast. Stuff each incision with a slice of mozzarella and a sun dried tomato, then season each breast and drizzle with olive oil. Transfer to a baking tray.
In a bowl add the gnocchi and pesto and mix together well. Tip onto the baking sheet, in and around the chicken. Scatter over the tomatoes and onion then bake everything for 25 minutes or until the chicken is cooked through and the gnocchi crispy and golden.
Serve right away with some basil leaves scattered over the top.