Toast the sesame seeds in a dry pan over medium heat for 3 to 4
minutes, shaking the pan gently, until the seeds are golden brown;
remove the seeds from the pan at once to prevent burning.
Crush the seeds in a food mill or with a mortar and pestle.
Combine the oils in a small bowl and pour about half into a wok or a
large heavy-based frying pan.
Heat over moderately high heat.
Stir-fry the onion, garlic, chili and prawns for 2 minutes; remove
from pan and set aside.
Stir-fry the tofu, tossing it occasionally until it is lightly
golden; remove from the pan and set aside.
Add the remaining oil to the pan and add the mushrooms and red
pepper; stir-fry for 3 minutes or until just crisp.
Add the water, soy sauce, sugar and boodles to the pan.
Toss gently to separate and coat the noodles in liquid.
Cover and steam for 5 minutes; toss well.
Add the prawns and tofu; toss for 3 minutes over medium heat.