Preheat the oven to 200C/400F/Gas 6.
For the lamb, rub the lamb with one tablespoon of the olive oil and season well with salt and freshly ground black pepper.
Heat a griddle pan until smoking hot. Add the lamb and cook for 2-3 minutes on each side, or until completely cooked through.
In a separate frying pan, heat the remaining tablespoon of oil. Add the peppers and onion and fry for three minutes or until softened.
Add the olives and tomatoes and cook for two minutes, then add the chargrilled lamb and warm through for one minute.
Stir in the basil, remove from the heat and keep warm.
For the boulangè re potatoes, melt 15g/½oz of the butter in an ovenproof frying pan over a low heat. Add the onions and fry for three minutes, until softened.
Add a splash of boiling water and continue to cook for one minute.
Place a 20cm/6in chefs' ring into the frying pan to hold all of the onion. Spoon in any extra onion from outside the ring.
Top the onion with the potato slices and finish with the remaining 15g/½oz of the butter.
Season well with salt and freshly ground black pepper and pour the stock over the potatoes. Transfer to the oven and cook for ten minutes, or until the potatoes are cooked through and golden-brown on top.
To serve, slide the potato boulangè re onto a plate and remove the chefs' ring. Place the lamb alongside and spoon over the pan juices.