MIx barbecue sauce and 1/4 cup dressing until blended.
Heat remaining dressing in electric pressure cooker using SAUTÉ setting on medium heat. Add onions and chili powder; cook and stir 2 min. Add meat and barbecue sauce mixture. Close and lock lid. Turn Pressure Release Valve to Sealing position.
Cook 40 min using HIGH PRESSURE COOK setting. When timer goes off, use Quick Pressure Release to carefully release pressure. Slowly remove lid. Use tongs to remove meat from cooker; cool slightly.
Meanwhile, skim and discard fat from surface of barbecue sauce mixture in cooker; cook 10 min. using SAUTÉ setting on high heat. While sauce is cooking, cook potatoes as directed on package.
Spoon meat over the potatoes; drizzle with 1/2 cup of the sauce. Sprinkle with parsley. Serve any remaining sauce on the side.