Can be seen in Kazordoon. It is the best food available in the game considering recovering time/weight. It's one of the best foods for long trips since they are light and provide a good regeneration rate. 100 fire mushrooms weights 10 oz. and will last you for 12 hours.
Regeneration:
One Fire Mushroom will regenerate hp/mana for 432 seconds (makes you 36% full).