Freeze 2 lbs sirloin steak for 1 hour.
Cut steak into thin strips against the grain.
Mix 5 tbsp soy sauce, 5 tbsp water, 1/4 cup green onion, 1/4 cup Splenda, 1 tbsp sesame oil, 1 tbsp minced garlic, and 1/4 tsp black pepper in a Ziplock bag.
Add the steak to the bag and shake.
Marinate for 1 hour.
Heat a skillet on medium-high heat.
Empty the marinated sirloin and juices into the skillet.
Brown the steak (it will cook quickly based on how thin it is cut).