Preheat oven to 350 degrees F (175 degrees C). Lay chicken breasts onto a baking sheet and sprinkle with 1 tablespoon taco seasoning mix. Bake for 30 to 35 minutes, cool and shred or cut into strips.
While the chicken is cooking, heat oil in a stockpot and cook the onions and celery until soft. Stir in the water and chicken broth. Season with cumin, black pepper and remaining taco seasoning mix. Simmer for 30 minutes for the flavors to mingle. Add the tomatoes, cilantro and chicken, simmer for 5 more minutes. Serve hot topped with avocado, shredded cheese and crushed tortilla chips.
