Stir the soup, sour cream, picante sauce and chili powder in a medium bowl.
Stir 1 cup picante sauce mixture, chicken and cheese in a large bowl.
Spread about 1/4 cup chicken mixture down the center of each tortilla. Roll up and place seam-side down in a 3-quart shallow baking dish. Pour the remaining picante sauce mixture over the filled tortillas. Cover the baking dish.
Bake at 350°F. for 40 minutes or until the enchiladas are hot and bubbling. Top with the tomato and onion.