Slow-Cooker Mongolian Beef

In a 4- or 5-qt. slow cooker, combine first 8 ingredients. Add beef and toss to coat. Cook, covered, on low 4-5 hours, until meat is tender. , In a small bowl, mix cornstarch and water until smooth; gradually stir into beef. Cook, covered, on high until sauce is thickened, 15-30 minutes. Serve over hot cooked rice. Sprinkle with green onions and, if desired, sesame seeds.