1. Toss the thinly sliced steak with cornstarch until fully coated. Set aside for 10 minutes.
2. Heat 2 tablespoons of vegetable oil in a large skillet over medium-high heat. Sear the steak in batches for 2-3 minutes per side until crispy and browned. Remove and set aside.
3. In the same skillet, add the remaining oil and stir-fry the carrots and red bell pepper for 3-4 minutes until tender-crisp. Add garlic and cook for 1 minute.
4. In a small bowl, whisk together soy sauce, brown sugar, rice vinegar, sesame oil, grated ginger, and red pepper flakes. Pour the sauce into the skillet and bring to a simmer.
5. Return the cooked beef to the skillet, tossing to coat evenly in the sauce. Simmer for 2-3 minutes until the sauce thickens slightly.
6. Serve over steamed rice and garnish with sesame seeds and chopped green onions.