Cut the potatoes into large wedges, then toss well in a large bowl with 2 tbsp of the olive oil and some salt. Spread the wedges out on a baking tray.
Fry the onion and garlic in the remaining olive oil over a low heat until soft and translucent. Add the tomatoes, butter beans, and some seasoning. Simmer for a few minutes, then pour into a baking tin or dish.
Mix a pinch of salt with the herbs. Stuff equal amounts under the skin of each chicken thigh. Put a slice of lemon on top of each thigh, then arrange on top of the tomato and bean mixture in the baking tin.
Bake the wedges and chicken traybake in the oven at 180C/160C fan/gas 4 for 45 mins until the chicken is cooked through. Check the potatoes after about 30 mins, shaking them around in the tray – depending on the size of the wedges, they may already be cooked through.15