2green onions(sliced, more for garnish if desired)
Combine sauce ingredients in your slow cooker/crock pot: soy sauce, water, fresh ginger, minced garlic, brown sugar, crushed red pepper flakes, cornstarch. Stir until well combined. Add sliced beef, stir until well coated with the sauce. Add sliced green onions and stir all of the ingredients together once more before cooking.
Heat on high heat for 2 hours, or on low heat for 4 hours. Serve over a bed of rice, and garnish with additional sliced green onions and/or sesame seeds (if desired).