Preheat oven to 400 degrees. Highly season the lamb shanks on both sides with salt and pepper. Heat 1/2 cup oil in a large Dutch oven. Dredge the shanks in the flour, shake off any excess flour. Sear the shanks on both sides until golden brown. Add the onions, fennel, and garlic. Cook for 4 minutes, moving everything around to ensure it's all cooking. Add the wine, tomatoes and stock. Bring to a boil, cover and place in the oven.
Cook for 1 1/2 hours or until the meat is so tender it falls from the bone. Adjust the seasonings. Remove from the Dutch oven and place on a platter. Top with chopped oregano, olives, and feta.