Prepare Marinade: In a bowl, combine soy sauce and cornstarch. Add steak and shrimp, mix well and marinate for 15-20 minutes.
Heat 1 tablespoon vegetable oil in a large skillet over high heat. Add marinated steak in a single layer and cook 2-3 minutes until browned. Remove and set aside.
Add another tablespoon vegetable oil if needed. Cook marinated shrimp 2-3 minutes until pink and opaque. Remove and set aside.
In the same skillet, stir-fry bell pepper, broccoli, and carrot for 3-4 minutes until tender-crisp.
Add garlic and ginger, cook 1 minute until fragrant.
Return steak and shrimp to skillet with vegetables. Toss and cook 1 minute to heat through. Season with salt and pepper.
Garnish with chopped green onions and sesame seeds before serving.