Heat olive oil in a large Dutch oven. Add onions, carrots, and celery and heat over medium low for 10 minutes or until onions start to brown. Add the garlic and cook for 30 seconds. Add the chicken stock, canned tomatoes with their puree (or fresh tomatoes), jalapenos, cumin, coriander, 1 tablespoon salt (depending on the saltiness of the chicken stock), 1 teaspoon pepper, and the cilantro and corn, if using. Bring the soup to a boil, then lower the heat and simmer for at least 25 minutes. Add tortilla strips and simmer for 5 more minutes or so. Add the shredded chicken and season to taste. Serve the soup hot topped with sliced avocado, a dollop of sour cream, grated Cheddar cheese, and broken tortilla chips.