Combine first 10 ingredients in large stockpot; cover with 5 cups water. Set pot over medium-high heat and bring to a boil. Reduce heat to medium-low and simmer 30 minutes, or until meat is cooked through.
Remove meat, chop into small pieces and set aside. Strain broth to discard chilies and return to pot. In a small bowl, whisk together cornstarch and 1 cup broth until smooth. Bring remaining broth to a boil; whisk in cornstarch mixture until broth is thickened. Return meat to broth and toss to coat evenly.
Place a large skillet over medium-high heat and coat with nonstick cooking spray. Add tortillas (1 or 2 at a time) and toast briefly, 1 to 2 minutes per side. To assemble, place 2 tortillas on each plate. Spoon meat mixture onto center of each. Top with lettuce, cheese and avocado. Garnish tops with sprigs of fresh cilantro.
All materials for this recipe are courtesy of www.delish.com