In a shallow dish, mix flour, cornstarch, 1 teaspoon salt and 1 teaspoon pepper. Add beef, a few pieces at a time, and toss to coat. In a large skillet, heat oil over medium-high heat; brown meat in batches. Transfer meat to a 5- or 6-qt. slow cooker. In the same skillet, cook and stir onion in drippings until tender, 6-8 minutes; add to slow cooker. Stir in broth, pumpkin, barley and seasonings. Cook, covered, on low until meat is tender, 6-8 hours. If desired, serve with additional red pepper flakes and parsley.