Heat the oven to 350°F. Press the tortillas into the bottoms and up the sides of 12 (2 1/2-inch) muffin-pan cups.
Stir the soup, sour cream, picante sauce, chili powder, chicken and cheese in a medium bowl. Divide the chicken mixture among the tortilla cups.
Bake for 20 minutes or until the chicken mixture is hot and bubbling. Sprinkle with additional cheese, if desired. Let the enchilada cups cool in the pan on a wire rack for 5 minutes. Top with the tomato and green onion before serving, if desired.