In a medium bowl, combine shrimp, soy sauce, rice vinegar, and cornstarch. Toss to coat and let marinate for 5 minutes.
Heat vegetable oil in a large skillet or wok over medium-high heat. Add the marinated shrimp and cook for 2-3 minutes until they turn pink and opaque. Remove shrimp from the skillet and set aside.
In the same skillet, add bell pepper, snap peas, garlic, and ginger. Stir-fry for 3-4 minutes until vegetables are tender-crisp.
Return the shrimp to the skillet and add hoisin sauce, red pepper flakes, and peanuts. Stir well to combine and heat through for another 2 minutes.
Garnish with sliced green onions before serving.