1. In a large sauté pan, heat olive oil. Add onion, garlic, and cilantro; sauté until golden brown. Add onion mixture to food processor with tomatoes; process until smooth. Return to pan and add cumin, pepper, and corn masa. Cook (stirring frequently) until thickened, about 5 minutes.
2. In a large saucepan bring chicken stock to a simmer. Add tomato mixture to hot chicken stock and blend until smooth (using an immersion blender if desired). Add squash, salt, and pepper and bring to a simmer. Cook until slightly thickened, about 15-20 minutes.
3. Add corn, black beans, chicken, and lime juice; heat through, about 2–3 minutes. Ladle soup into bowls. Top with cheese, sour cream, avocado, tortillas and fresh cilantro.