Sauté diced onion and minced garlic in oil in a pan for 5-7 min, or until translucent.
Add onions to crockpot with remaining ingredients (excluding tortillas and avocado) and cook on high for 4 hours.
After about 3 1/2 hours, remove chicken breasts and use two forks to pull apart/shred on a plate.
Once completely shredded add back into crockpot along with 2 sliced tortillas (into 2-inch long, thin strips) to cook another 20 minutes.
Tortilla crisps: cut remaining tortillas into long strips, lay flat on baking sheet, spray with olive or avocado oil and season with sea salt & cumin. Toss together and spread out evenly. BROIL for 5-8 min on high, middle rack until starting to turn crispy.
Serve tortilla soup with tortilla crisps and sliced avocado.