Prepare the marinade in a bowl by combining soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, and black pepper.
Add the thinly sliced ribeye to the marinade, making sure all pieces are coated well.
Preheat your oven to 425°F (220°C) while the beef marinates.
Line a large sheet pan with parchment paper for easy cleanup and place the marinated beef on it, spreading it out evenly.
Add the sliced bell pepper and onion to the pan, distributing them around the beef.
Roast in the preheated oven for 15-20 minutes, stirring halfway through.
Once cooked, remove the pan from the oven and sprinkle chopped green onions on top before serving.