Preheat oven to 360°F/180°C degrees and heat a large earthenware casserole dish on the stovetop.
Season the lamb shanks with sea salt and pepper. Add the olive oil to the dish and sear the lamb shanks for 3 minutes on all sides.
Remove the lamb shanks and add the chopped onion and the garlic. Cook for 2- 3 minutes until softened then add the red wine and the sprig of rosemary. Reduce wine by half, add cherry tomatoes and crushed tomatoes. Return the shanks to the pan and bring to the boil.
Cover dish with some foil and a lid and place in a medium oven (360°F/180°C degrees) for 1 hour and 30 minutes.
After 1 hour 20 minutes remove from the oven and with a small knife test that the meat is cooked through and falling off the bone. Depending on the actual size of the shanks they may need up to another 30 minutes to cook.
Carefully remove the shanks from the sauce and set aside. Add the sliced green zucchini, buckwheat and green olives to the sauce and stir through, adjust seasoning with sea salt and pepper.
Spoon the sauce over the shanks and garnish with the fresh sage leaves. Serve with steamed seasonal vegetables.