In the pressure cooker, it takes only 20 minutes to make homemade chicken stock. Ground red chiles found in Mexican markets are quite different from regular chili powder or ground red pepper. You can substitute ground New Mexico chile powder.
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.