Cook the spaghetti in boiling salted water until tender. Drain, rinse, place on a serving dish and keep hot.
Melt the butter in a saucepan. Add the onion and celery; fry gently until tender.
Stir in the flour and cook for a few minutes. Add the tomato soup, water and 4oz. (115g) shredded cheese. Stir until the sauce thickens and the cheese is melted.
Add the tuna, peas, salt and pepper. Reheat.
Pour the sauce over the spaghetti and sprinkle with the remaining cheese.
Recipe by Country Recipe Book at https://countryrecipebook.com/spaghetti-with-tuna/