Puree avocado, lime, Greek yogurt, cilantro and sugar. Taste and adjust seasoning, if necessary.
Place in the refrigerator. Preheat oven to 375 degrees. Combine the corn chips, chili powder, cumin, smoked paprika and red pepper flakes/cayenne in the bowl of a food processor. Pulse until mixture resembles bread crumbs.
In a separate small bowl, whisk together egg and milk. Season chicken breast cubes with a dash of salt and pepper. Prepare baking sheet with a wire rack and coat with cooking spray.
Dip chicken breast cubes into the egg/milk mixture, then coat with the corn chip/spice mixture. Place on the wire rack with at least an inch of space in between each nugget.
Coat each nugget with cooking spray. Place in the oven and bake for 12-14 minutes, until internal temperature of nuggets reaches 160 degrees. Allow nuggets to cool for a few minutes before eating. Serve with avocado yogurt dip.