Cut some slices of red onion.
Squeeze the juice of two fresh limes into a bowl. Add onions.
Cut up fresh Cilantro and add in. Set aside to marinade for at least 45 minutes.
This KILLER sandwich is a Trader Joe's Veggie Burger (the best one I have found outside of Northstar Cafe!!) Add some Hummus and then top with the pickled onions.