- Preheat oven to 230°C.
- Wash leg of lamb.
- Slit with a sharp knife in various places on both sides of lamb.
- Insert garlic slices in slits.
- Season with salt, pepper, add ½ tablespoon oregano, and brush with olive oil.
- Pour lemon juice over lamb and place in roasting pan, fat side up.
- Roast for about ½ hour.
- While lamb is browning, combine salt, tomato paste, and water and pour over potatoes.
- Add to roasting pan; sprinkle with remaining oregano.
- Lower oven temperature to 180°C.
- Roast for 1½ hours, turning and basting the potatoes occasionally.
- Remove to a hot serving platter; slice and serve meat surrounded by potatoes.