Vegetarianism linked to spread of Buddhism? The Buddha was neither a vegetarian nor did he ask anyone to be vegetarians! The idea was that, one should not consume meat from an animal killed only specifically for oneself. This has to do with non-violence, nothing to do with vegetarianism.
Islam did not inspire biriyani. The discovery of biriyani was a chance discovery of Mughal army cooks under command of Aurangzeb who had to prepare food with limited ration (meat, potato, rice).