You receive this quest from Gaptooth in the River of the Addancs during the Blow up the Dam quest.
Gaptooth says to bring him 30 Bannock Buns, then he'll blow up the dam.
To get the 30 Bannock Buns, get a nice start by heading to the middle part of the Mounds Zone and touch the statue. It will give you 10 Bannock Buns.
Then, to get the rest, go to the different cities on the Island and visit their Inns. Remember to save before going into each inn, and if they dont have at least 3-4 Bannock buns, keep reloading that save until they do.
You will need to do that for the next 1-2 days depending on how many Bannock Buns you started out with.
Once you have 30 Bannock Buns, return to Gaptooth in the River of the Addancs.
The Bring Bannock Buns quest will be solved.
You will lose 30 Bannock Buns and your health will be decreased by 10.