As described above: Half board includes breakfast and a 5 course evening meal. It does not include lunch or any drinks.
Half board in most places, including the Zanzibari, means breakfast and evening meal. At the Zanzibari you have a choice of numerous things for breakfast and after breakfast you chose what you want for dinner/evening meal. This is done to avoid wasting unwanted food. Food is available at lunch time if required in the bar/restaurant. By the way we thought the food was really good, especially the Swahili buffet.
Get an answer from The Zanzibari staff and past guests.