School dinners are a minefield, as Jamie Oliver discovered when he came up against mothers defiantly pushing burgers through the fence to their chicken-nugget deprived offspring. It’s fine to change your curriculum, sack your headteacher, flatten buildings and replace them with uglier ones, but mess with the lunches and you’d better put on your tin hat. So when MUSE school in Calabasas, California, decided to become the first …