In a large bowl, combine the sliced steak and shrimp. In a small bowl, mix the soy sauce, oyster sauce, cornstarch, water, and sesame oil. Pour half of this mixture over the steak and shrimp, tossing to coat. Let marinate for 15 minutes.
Heat 1 tablespoon of vegetable oil in a large skillet or wok over medium-high heat. Add the marinated steak and cook for 2-3 minutes until browned. Remove from the skillet and set aside.
In the same skillet, add the remaining tablespoon of oil. Add the sliced bell peppers and snap peas, stir-frying for about 3-4 minutes until they are tender-crisp.
Add the minced garlic and ginger to the vegetables, stirring for an additional 30 seconds until fragrant.
Return the cooked steak to the skillet along with the shrimp. Pour the remaining sauce over the mixture and stir-fry for another 2-3 minutes until the shrimp are cooked through and everything is well combined.
Serve hot over cooked rice or noodles.