For the lamb, heat the olive oil in a frying pan, add the lamb, garlic, rosemary, salt and freshly ground black pepper and fry for 3-4 minutes on each side, or until golden-brown but slightly pink in the middle. Remove from the heat and leave to rest for five minutes, covered with aluminium foil.
For the ratatouille, heat the olive oil in a pan, add the onion, pepper, garlic and courgette and fry for five minutes, or until beginning to soften.
Add the tomato purée, salt and freshly ground black pepper and a splash of boiling water. Simmer gently for ten minutes.
To serve, spoon the ratatouille onto a serving plate and top with the lamb.