Heat oven to 220C/fan 200C/gas 7. Cut the peppers in half lengthways and scoop out the seeds and white membrane, but try to keep the stalk attached. Stuff each pepper half with basil (but don’t use it all), the garlic and a tomato half.
Snuggle the stuffed pepper halves alongside the chicken in a roasting tin. Drizzle the oil over everything and season with pepper and salt, if using. Roast the chicken and the peppers for 25-30 mins until the chicken is golden with crisp skin, and the peppers and tomatoes have softened and wrinkled. Lift the chicken and the stuffed peppers onto a plate, tipping the peppers so that the tasty juice drains into the roasting tin.
Place the tin over a low flame and pour in a splash of water. Add the beans and stir well to release any sticky bits from the roasting tray. Stir the remaining basil through the beans and spoon them alongside the chicken and peppers.