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 ¼ cup chicken mixture down the center of each tortilla. Roll up and place seam-side down in a 3-qt shallow baking dish. Pour the remaining picante sauce mixture over the filled tortillas. Cover the baking dish.
Bake at 350 for 40 mins or until the enchiladas are hot and bubbling. Top with the tomato and onion.