Child neglect at school should not be tolerated

My child does not eat school lunch because he is vegetarian and lactose intolerant. I send him a lunch to school of a chosen food he eats daily. The lunch has to be heated up but the principal does not allow students nor staff to use the microwave for a child's lunch. So my child has come home 3 days straight without eating and the school as well as the teacher is knowledgeable of his diet. In order for my child to eat I have to leave home go out to the school and heat his lunch up so that he can eat. I feel like it's highly inconvenient on my behalf and unfair to my child.