In a large skillet, cook beef and onion over medium heat until beef is no longer pink, 6-8 minutes, breaking up beef into crumbles; drain. Stir in beans, picante sauce and chili powder., In a bowl, combine soup, tomatoes and green chiles. In a lightly greased 2-1/2-qt. baking dish, layer half the chips, beef mixture, soup mixture and cheeses. Repeat layers., Microwave on medium-high, uncovered, until heated through and cheese is melted, about 12 minutes. If desired, top with avocado and sour cream.