In large saucepan, saute onion and garlic in 1 TBSP oil about 5 minutes, until onions are soft. Add tomatoes with green chilies, pureed tomatoes, chicken groth, chili powder, cumin and salt. Heat to boiling, reduce heat and simmer 20 - 30 minutes. Meanwhile, cut tortillas into thin strips and fry until crisp in 1/2 inch of hot oil; drain on paper towels (or you can use tortilla chips and eliminate this step). Add chicken, if desired, and tortilla strips to soup and heat through - about 5 minutes. Garnish each serving with sprinkling of diced avocado, cheese and a dollop of sour cream. Makes 8 servings.