Heat the grill to its highest setting and put a large saucepan of salted water on to boil. Tip in the pasta and cook for 1 min less than the pack suggests.
Meanwhile, make the sauce by simmering the tomatoes in a pan with a little seasoning and the thyme for about 5 mins. Pour in the cream, stir and simmer for another 4-5 mins.
Drain the pasta, reserving a little of the cooking water, and tip back into the saucepan. Pour over the creamy tomato sauce, the sundried tomatoes, sweetcorn and tuna. Layer into a baking dish (ours was 22 x 29cm), scattering over the grated cheddar between layers. Sprinkle the Parmesan on top and put under the grill for 5 mins until bubbling and golden.