Cut the lamb into large pieces, discarding any excess fat. Mix the oregano with the garlic and a little seasoning and rub into the lamb.
Heat half the oil in a large saucepan or sauté pan and fry the lamb in batches until browned. Drain to a plate.
Add the aubergine to the pan with the onions and remaining oil and cook very gently, stirring frequently, for about 10 minutes until softened and lightly browned. Return the meat to the pan with the wine, tomatoes, honey, olives and seasoning. Cover with a lid and cook on the lowest setting for about 1¼ hours or until the lamb is very tender. Lightly toast the bread and spoon the tzatziki on top.
Check the stew for seasoning and turn into shallow bowls. Serve with the toasts on the side.