I've only ever had their eggplant sandwich, and that's the only thing I will ever want-need-crave from them. It is a filling sandwich, great for people with big hands. Those with smaller hands will find themselves getting a.. good bang for their buck here.
The price of their popular sandwiches keep going up. I will occasionally allow myself to keep buying their eggplant sandwich, though. Life wouldn't be the same if I didn't have the freedom to munch and crunch on their more-crunchy-than-soggy deep-fried breaded eggplant yumminess, loaded with extra veggies -- onions, green peppers, and a leaf of lettuce and slice of fresh tomato as well.
They offer it on either "focaccia" bread or on a big bun (maybe you can wear baseball or oven mitts, if you like me have small hands). A very suitable 'wich for Wolverine if ever you're lucky enough to interact verbally w/ him.
One half of their hefty sandwich usually does the trick in keeping my belly full. Maybe bring along another friend? That way, you'll be leaving enough room for some fresh fruit or whatever small dessert-like nibblies that your heart may be desiring. Maybe some cubes of cheese from one of the cheese shops, or a very freshly baked bagel from St. Urbain bagels. You'll find tons of snack options at St. Lawrence Mkt.
Mustachio is located on the basement level of the St. Lawrence Market South building. Closed Sundays, methinks.
4.5 stars. Let me know if their prices ever drop.