Sprinkle chicken with cumin; toss well. Spread salsa evenly over bread shells to within 1/2 inch of edges; arrange chicken over salsa. Layer beans over chicken; sprinkle with cheese. Place pizzas on a large ungreased baking sheet.
Bake at 450° for 10 minutes or until cheese melts and crust is golden; sprinkle with green onions. Top each pizza with 1 tablespoon sour cream, if desired. Serve immediately.