Preheat oven to 350°.
Cut each tortilla in half. Cut tortilla halves into 1/4-inch strips. Arrange tortilla strips in a single layer on a baking sheet. Bake at 350° for 6 minutes or until lightly browned, stirring after 3 minutes. Cool completely.
Combine onion and next 9 ingredients (onion through bay leaf) in a 6-quart pressure cooker. Close the lid securely; bring to high pressure over high heat. Adjust heat to medium or level needed to maintain high pressure; cook 20 minutes. Remove from heat; place cooker under cold running water. Remove the lid. Remove chicken from broth; cool slightly. Remove chicken from bones; cut meat into bite-sized pieces. Discard bones.
Strain stock through a sieve into a bowl, and discard solids. Return stock to cooker; stir in ground chiles, oregano, cumin, and chicken; let stand 5 minutes.
Divide tortilla strips evenly among each of 8 bowls; top each serving with about 1 1/3 cups soup, 2 tablespoons avocado, 1 tablespoon sour cream, and 3/4 teaspoon cilantro.