Heat oil in a wok or large non-stick pan over medium heat for about 1 minute.
Add minced garlic and ginger and stir for about 5 seconds.
Add chopped onions and stir for another 5 seconds.
Add carrots, string beans, and 1 tbsp water to the pan and mix. Cover with a lid and leave to steam for about 3-5 minutes.
Add red and yellow bell peppers and continue to stir vegetables for about 2-3 minutes.
Stir in broccoli with the other vegetables. Let cook for about 3 minutes.
Add oyster sauce, soy sauce, wok sauce if using, sesame oil, and salt to taste.
Mix vegetables for about 2 more minutes, then turn off the heat.