Heat oil in heavy large pot over medium heat. Add garlic and stir 20 seconds. Add chicken and oregano to pot; sprinkle with salt and pepper. Sauté 3 minutes. Add broth and lime juice and bring to simmer. Reduce heat to medium-low and simmer gently until chicken is cooked through, about 8 minutes. Season soup to taste with salt and pepper.
Divide crushed tortilla chips among 6 bowls. Ladle soup into bowls. Top soup with avocados, tomatoes, green onions, cilantro and jalapeños. Garnish with lime slices and serve.