Combine all ingredients in a large bowl or zip lock bag. If you are about to cook it, let it marinate at the very least for 15-30 minutes. If you are making this ahead, cover and refrigerate for 30 minutes before cooking.
In a large nonstick skillet, add 1 tbsp of oil over medium-high heat. Add thin sliced onions and peppers and stir fry for about 1-2 minutes.
Then, add the beef and stir fry until browned and to the doneness you prefer. Remove from heat, sprinkle with green onions, and serve with rice.