Avocado relish has many of the same ingredients as guacamole, such as cilantro, lime juice, onion, and salt. Instead of mashing the avocado, it is diced with the other ingredients.
Avocado relish tends to be a lot crunchier and tangier than guacamole. Its texture and use of pickled jalapenos instead of fresh classifies it as a relish instead of guacamole.
It's often used on grilled meats or as a condiment, and when it comes to tortilla soup, avocado relish adds a bright, fresh element to the rich, spiced dish.