Cut tortillas in half, then cut halves crosswise into 1/4 inch thick strips. In 4-quart saucepan, heat oil on medium until shimmering. Add one-third of tortilla strips. Cook 3 to 4 minutes or until golden and crisp, stirring. With slotted spoon, transfer to paper towels to drain. Repeat with remaining tortillas in 2 batches. Discard oil in pan.
To same saucepan, add salsa. Cook 3 minutes or until thickened. Stir in broth and water and heat to boiling. Reduce heat to maintain gentle simmer. Submerge chicken and half of tortilla strips in liquid. Cover and cook 12 minutes or until chicken is no longer pink in center. With slotted spoon, transfer chicken to plate. With 2 forks, shred chicken into bite-size pieces. Transfer soup to blender and puree until smooth. If necessary, return soup to pot and rehat.
Divide soup and chicken among bowls. Top with sour cream, avocado, and remaining tortilla chips.
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