Combine the sliced beef with baking soda, cornstarch, and gochujang in a bowl. Toss to coat evenly and let sit for 10 minutes while you prep the remaining ingredients.

Whisk together all the sauce ingredients (2 tbsp soy sauce, oyster sauce, beef broth, 3 tbsp soy sauce, dark soy sauce, and mirin) in a small bowl and set aside.

Heat vegetable oil in a wok or large skillet over medium-high heat. Add the onion and carrot and cook for 1 minute. Stir in the garlic for 30 seconds. Add the marinated beef, spread it out in a single layer, and sear for 2 minutes without stirring. Toss and cook for 1 additional minute.

Pour in the sauce and mix thoroughly until everything is well coated. Add the green onions and toss to combine. Drizzle with sesame oil, remove from heat, and garnish with sesame seeds. Serve immediately over steamed rice.