Aloha from Kaua'i!
Today I finally got a chance to drive into Koloa and try the burritos at "Monster Tacos" - this is a lunch wagon that has been traveling around - in Hanapepe, etc., etc. - but I asked them and they are now more or less permanently located on Weliweli Road in Old Koloa town in front of the Kaua'i ATV offices (behind Island Soap and Candle and just before the Koloa Neighborhood Center).
Open every day but Sunday - she said they are now going to be there on Saturdays as well.
I had a black bean burrito with the "add on" of a hand-made tortilla ($1.00) and chips and salsa (another $1.00) - I think the burrito was $6.00 and my total was right around $8.00 - a huge burrito with a nice amount of heat to it and lots of good crunch from purple cabbage as well - definitely worth it and a whole lot of good, fresh food!
I think next time I will call ahead for pick-up - it was almost 2pm and there were still a few people in line ahead of me - since they make everything fresh, you do have to wait a little bit - or you can avoid it but calling them and picking it up. No place to eat there either - but I live only a couple of blocks away, so works for me!
Anywho - thought I'd give an update as they've been traveling around in various locations - this seems to be their "spot" at least for the forseeable future!