This recipe is the ideal super easy supper for families. Use any pasta that you have in the storecupboard but bows, penne or macaroni work best.
Preheat the oven to 160°C (325°F) mark 3. In a frying pan stir fry the onions for 1-2 minutes in a little oil. Drain the tuna well, and flake into a bowl. Cook the pasta in a pan of boiling water for about 10 minutes or until just cooked. Add the frozen peas and sweetcorn to the pan 5 minutes before the end of cooking.
To make the sauce, place milk, flour and butter in a small saucepan and whisk continuously over medium heat until the sauce begins to boil and thicken. Turn down the heat to its lowest and let the sauce cook for 2 minutes. Add the grated cheese and mustard, keeping a little cheese back for the topping. Season with a little lemon juice.
Mix the pasta with the vegetables, spring onion, tuna and cheese sauce and pour into a lightly oiled ovenproof dish. Sprinkle with the remaining cheese and bake in a preheated oven until golden on top, about 25 minutes. Serve with steamed green beans or broccoli.