Wash new potatoes and cut into quarters. Boil or steam them until tender-crisp (about 8-10 minutes, can be done simultaneously with beef cooking if pan is large enough).

Cut beef sirloin into 1-inch cubes. Mince garlic. Slice onion into thick wedges and bell pepper into strips.

In a small bowl, whisk together soy sauce, oyster sauce, sugar, rice vinegar, and black pepper to create the sauce.

Heat 5ml vegetable oil in a large skillet or wok over high heat until smoking. Add beef cubes in a single layer and sear for 1-2 minutes per side until nicely browned. Remove beef from pan and set aside.

Add remaining 3ml vegetable oil to the same pan. Add minced garlic and cook for 30 seconds until fragrant. Add onion wedges and bell pepper strips, stir-fry for 1-2 minutes until slightly softened.