For the sauce, mix together the ketchup, soy sauce, fish sauce, sweetener, powdered peanut butter mixed with water, lime juice and chilli flakes.
Cook the rice noodles according to the pack instructions (usually cover with boiling water for about 10 minutes) and set aside.
Spray a large frying pan with low calorie cooking spray, then add the sliced onions and diced chicken to the pan.
Cook until golden brown and the chicken is almost cooked.
Add the mixed stir fry vegetables, and cook for 2-3 minutes. Remove from the pan and set aside. Add a little more low calorie cooking spray to the pan.
Beat the eggs with a fork, then add to the frying pan and cook over a medium-high heat, stirring continuously until the eggs are scrambled. Don't over cook them, it's best to leave them a little wet.
Return the chicken and vegetables to the pan, add the cooked noodles, then pour the sauce over the top and stir well over a medium heat for a few minutes.
Sprinkle with some chopped coriander and serve.