Preheat fan oven to 180 and boil a large pan half full of water. Add salt to bring to boil faster. When bubbling furiously add pasta, keeping pan lid off.
When that is on the go heat a small splash of olive oil in a large, deep frying pan and chilli flakes without stirring. When they start to jump around in pan, add tomatoes and stir gently for 5 mins
Now add the sugar and some black pepper, stir and taste and adding only a little more if needed. Then tip in the tuna steaks and, once in sauce, separate until in shreds. Now simmer for a further 5 mins.
After that take check your pasta, which should be cooked, and if so take of the boil and drain. When drained stir in about 1/4-1/2 of the tomato sauce. Add pasta to bottom of baking dish and then top with the rest of sauce. Now add the mozzarella and top with parmesan. Bake for 30 mins.