In a skillet over medium heat, add oil. When hot, place beef cubes and sear until just brown, season with salt and freshly ground black pepper. Transfer beef and its juices to the crock pot and then add onions, pepper, tomatoes, garlic, ginger, sugar, hoisin, Worcestershire sauce, soy sauce, chili oil and beef stock; stir to combine.
Cook on “Low” for 7 hours or “High” for 3:30 hours. To thicken the sauce, add cornstarch mixture. Serve over a bed of rice, add some chopped chives and sprinkle with sesame seeds.