1. While the chicken defrosts, if necessary, heat the oil in a 4-1/2 qt Dutch oven or soup pot over medium heat. Peel the onion and finely chop it, adding it to the pot as you chop. cut the partially defrosted or fresh chicken into bite-size chunks, adding them to the pot as you cut. When all of the chicken has been added, raise the heat to medium-high and cook stirring, until the chicken is almost cooked through, about 3 minutes.
2. Peel carrot and slice into 1/4 inch thick, adding to pot as you slice. Finely chop celery and add to pot. Cook, stirring, until the vegetables are tender, about 3 minutes.
3. Add the broth and 4 cups water and raise the heat to high.
4. While the liquid is heating, slice the flour tortillas into thin (about 1/2 inch wide strips). When the liquid is at a boil, add the strips and cook until plumped up, 4 to 5 min. When they are plump, remove the pot from the heat and let stew stand for about 5 minutes to cool slightly. To serve, divide stew among four soup bowls.
*Note: You can use Chunky Seasoned Chicken prepared in advance and frozen--just defrost first. Cooked leftover turkey can also be used.