Add all marinade ingredients to a large bowl or ziplock bag, and stir to combine. Add the sliced steak, and toss in the marinade. Cover/seal and refrigerate for at least 15 minutes.
Pepper Steak
Heat 1 Tbsp. oil in a large saute pan over medium-high heat. Add the sweet peppers and white part of the scallions, ginger, garlic, and saute for 3 minutes, stirring occasionally. Transfer to a plate.
Add the remaining 1 Tbsp. oil to the saute pan. Remove half the steak from the marinade with a slotted spoon (reserving the marinade) and saute about 2-3 minutes until browned, stirring occasionally. Transfer steak to plate with the veggies. Saute the remaining steak, then transfer to plate.
Add the reserved marinade to the skillet and cook for 1 minute or until thickened. Add the steak, veggies and green parts of the scallions to the skillet, and stir to combine. Cook for an additional minute, then remove from heat.