Stir the soup, picante sauce, water, sour cream and chili powder in a large bowl. Reserve 3/4 cup soup mixture. Add the chicken to the remaining soup mixture and stir to coat.
Spoon 1/2 cup chicken mixture down the center of each tortilla. Fold the tortillas around the filling. Place the filled tortillas seam-side down into an 11x8x2-inch baking dish. Spoon the reserved soup mixture over the filled tortillas. Sprinkle with the cheese, if desired. Cover the baking dish.
Bake for 35 minutes or until the enchiladas are hot and bubbling. Garnish with the tomato and green onions, if desired.