Heat a little oil in a wok over medium heat. Add the chicken, then crumble over the stock cube and add the chilli powder. Stir fry until chicken is no longer pink in the centre, 5-10 minutes.
Add the onions, carrots, capsicums, mushrooms and garlic. Stir fry over high heat 5-10 minutes until softened but not browned. Reduce heat to low while you make the sauce.
Put the peanut butter and soy sauce in a small saucepan over low heat and stir well. Gradually stir in the milk, a spoonful at a time. Pour into the wok and mix well. Add the bamboo shoots and water chestnuts.
Meanwhile, cook the egg noodles in boiling salted water about 4 minutes or until soft, then drain and add to the wok. Serve immediately.