Will he eat cold meets on a sandwich or wrap? You could make and freeze some rolls/sandwiches.
Could you make some fruit muffins if he only eats fruit that's been cooked in something?

Salads perhaps?

If the school has a healthy policy (eg: no chips), you could get some pita bread and put some herbs and oil on it to flavour it and then heat it in the oven until it's crispy and break it up into chips for a healthy alternative to chips. This is something he could help make too.

What about making some pizza scroles. I saw a recipe the other day where you cut puff pastery into strips and add tomato paste and a few diced toppings (ham, pineapple etc-whatever you like) and then roll each strip tightly and bake in the oven. The recipe does call for cheese as well but you could skip this if he's allergic.