Chop all vegetables before beginning to cook.
Heat both sesame oil and vegetable oil in a large wok until almost smoking.
Add the onion and stir-fry over high heat for 1 minute or until soft.
Add the garlic, ginger and red and yellow peppers and snap peas. Toss for a further 2 minutes until peppers are just beginning to soften.
Add the mushrooms and continue to toss over high heat for 2 minutes.
Add remaining ingredients and cover for 1 to 2 minutes to steam bok choy.