Delicate chicken breast fillets are quite dry, and the vegetables add flavor and moisture. Just bake them together in the oven, and a delicious dinner is ready.
Preheat the oven to 220C/200C Fan/Gas 7. Heat the butter and oil together in a shallow, flameproof casserole over a low heat. Add the onion and cook for 5 minutes, stirring regularly until softened.