Cut out and discard the end of each zucchini half. Cut a 1/4” slice from each half to make a cover. Scoop the flesh from the remaining part and make each half a shell of 1/4” thickness. Finely chop the zucchini flesh, onion and canned tomato. Grate the Cheddar cheese. Melt half of butter in a frying pan with medium heat. Add the chopped vegetables and basil, and stir fry for 5 minutes. Simmer the stock in another pan. Take out the frying and melt the other half of the butter. Add the rice and stir. Add 2 tablespoons of stock to the rice, and stir until the stock is fully absorbed. Repeat with the remaining stock, and keep stirring to prevent the rice from sticking to the pan. Cook for about 25 minutes until the rice is cooked and becomes a creamy risotto. Add the fried vegetables and stir to combine. Turn off the heat, add the cheese and blend it with the risotto. Stuff the zucchini shell with the risotto, and place the cover on the top. Preheat the oven to 200 centigrade degree and bake the stuffed zucchini for 20 minutes.