Preheat your oven to 325°F (160°C) and ensure the oven rack is in the lower third position to accommodate the roast.

In a small bowl, combine the minced garlic, olive oil, lemon juice, dried oregano, salt, and black pepper to create a thick marinade paste.

Using a sharp knife, make small slits all over the surface of the leg of lamb, about 1 inch deep.

Rub the marinade paste thoroughly over the entire leg of lamb, pushing some of the mixture into the slits for deeper flavor.

Place the lamb into a deep roasting pan and pour the cup of water into the bottom of the pan to create steam and prevent burning.

Cover the roasting pan tightly with heavy-duty aluminum foil to seal in the moisture completely.

Roast in the preheated oven for 3.5 hours, or until the meat is extremely tender and pulling away from the bone.

Remove the foil and increase the oven temperature to 400°F (200°C) to crisp up the exterior.

Roast uncovered for another 20 to 30 minutes until the top is golden brown and slightly crispy.

Remove the lamb from the oven and let it rest for at least 15 minutes before carving to allow the juices to redistribute.