Preheat the oven to 350 °F.

Use a sharp knife to cut slits into the leg of lamb. Stick the garlic slivers into the slits.

Place the lamb in a large roasting pan.

Combine the lemon juice and olive oil together and pour it all over the lamb. Season the lamb on both sides with salt, pepper, and oregano.

Add the rosemary sprigs and the onions to the pan. Pour the water into the pan.

Cover the lamb with a sheet of parchment paper and then tightly with aluminum foil.

Bake for 3-4 hours or until the meat is soft and almost falling off the bone.

Remove the foil and parchment and place the pan back into the oven and onto the middle rack. Turn the broiler element on and broil for 5-10 minutes or until the top is golden.