In a large saucepan, heat the olive oil over medium-high heat. Stir in the onion and garlic, lower the heat to medium and cook until the onion begins to brown, about 7 minutes. Increase the heat to high, push the vegetables to the side of the pan, add the chicken and cook, stirring, until golden, about 5 minutes. Stir in the chipotles and adobo sauce, then stir in the chicken broth. Lower the heat and simmer for 15 minutes, skimming any foam. Stir in the cilantro and lime juice; season with salt and pepper.
Place 2 avocado slices in each of 6 soup bowls and pour in the soup. Top with the tortilla chips.