Here's a favorite healthy lunchbox meal of my children's. I prepare it in the evening and pack it for them to eat at school the next day, but it's so quick and easy that you can even prepare it in the morning so that the children can take it fresh with them. The primary school has a refrigerator and microwave oven, so I'm not concerned about food going off in their bag before lunchtime.
Open a small tin of tuna, and drain it of the oil or brine. Do likewise with a small tin of corn (not the creamed variety). Boil some pasta (enough for two servings) till al dente. When cooked, pour in the tuna and corn. Don't add salt. Add two full tablespoons of mayonnaise and mix everything together. Finally, sprinkle some grated cheese over the dish.
Without the pasta, the same corn and tuna mix can be used as a sandwich spread, on buttered wholewheat bread triangles, with cheese added.