My boyfriend is the one who introduced me to Irazu, which is located in Chicago and serves Costa Rican food. Here, I'll give you his recommendations for vegan ordering while dining at Irazu.
First of all, get the oatmeal shake made with water. Don't get soy milk, just water. This is one of my favorite parts of going to eat at Irazu. The oatmeal shake (pictured) is sweet and cinnamon-flavored and pretty darn filling on its own! You should also get a Vegetarian Taco. It's $2.95 and you don't need more than one. If you're really hungry, get an order of Yucca Fries, which come with a garlic oil for dipping. Add to that a bottomless basket of chips and a squeeze bottle of salsa and you're set for a delicious meal at a low price (but remember that they only take cash!).
The one additional thing that is a great treat when they have it is the Lava Juice, which is just watermelon juice! Refreshing and tasty!