Heat a three litre capacity ovenproof dish (with a lid) over a medium heat. Add the olive oil, onion, sausage, garlic and sea salt and stir for five minutes, or until the onion is soft and translucent.
Add the rice to the dish and stir for another minute. Add the stock or water and the chopped tomatoes and bring to simmering point. Stir in the tuna, zucchini and season with black pepper.
Cover the dish and bake the risotto in the pre-heated oven for thirty minutes, or until the rice is cooked. Stir in the olives.
Scatter parsley over the top, sprinkle with finely grated Parmesan if desired, and serve in the dish.