Slice the beef sirloin thinly against the grain and set aside.

Prepare all vegetables by washing and slicing them as indicated.

Heat vegetable oil in a wok over high heat.

Add the sliced beef and stir-fry for about 3-4 minutes until browned.

Add the broccoli, bell pepper, carrots, and snap peas to the wok and stir-fry for another 3-4 minutes.

In a small bowl, mix together soy sauce, oyster sauce, and cornstarch with a little water to create a sauce.

Pour the sauce over the stir-fried beef and vegetables, stirring well to combine and cook for an additional minute.

Drizzle with sesame oil before serving.