If I had a child who received such a notice from a government school, I would ask my pediatrician to write the following:
Please excuse little Johnny from school lunches. As his physician, I have decided he may eat only the lunches packed by his mother. Sadly, little Johnny is allergic to bureaucratic stupidity and banana republic-style dictatorships, and he requires a special diet of freedom, as exemplified by whatever his mother chooses for his lunch.