Cut lamb into 2-inch cubes. Heat oil in a thick-bottomed heatproof casserole and brown lamb on all sides; add chopped onion and cook until lightly browned. Add tomatoes and tomato concentrate dissolved in a little water, and season to taste with chopped parsley, oregano, salt and freshly ground black pepper.
Bring to a boil; reduce heat and cover casserole; simmer gently for 1 hour. The