Prepare the ingredients: Rinse the shrimp under cold water and pat dry with paper towels. Slice the bell pepper, and wash the broccoli and snap peas.
Heat the wok or large skillet over medium-high heat and add the vegetable oil. Once hot, add the minced garlic and stir-fry for about 30 seconds until fragrant.
Add the shrimp to the wok, cooking for about 2-3 minutes or until the shrimp turns pink and opaque. Remove the shrimp from the wok and set aside.
In the same wok, add the sliced bell pepper, broccoli florets, and snap peas. Stir-fry the vegetables for about 4-5 minutes until they are tender-crisp.
Return the shrimp to the wok. Add the soy sauce, oyster sauce, and sesame oil, stirring to coat everything evenly.
Pour in the cornstarch mixture to thicken the sauce. Stir constantly for 1-2 minutes until the sauce has thickened.
Season with salt and pepper to taste. Remove from heat.
Serve the shrimp stir-fry over cooked rice or noodles, garnished with sesame seeds if desired.