Heat the oven to 350°F. Stir the soup, sour cream, picante sauce and chili powder in a medium bowl.
Stir 1 cup soup mixture, chicken and cheese in a large bowl.
Divide the chicken mixture among the tortillas. Roll up the tortillas and place seam-side down in an 11 x 8 x 2-inch baking dish. Pour the remaining soup mixture over the filled tortillas. Cover the baking dish.
Bake for 40 minutes or until the enchiladas are hot and bubbling. Top with the tomato and onion.