In a small plate, combine mustard and mayonnaise. Set aside.
Remove the sinew/tendon from the chicken tenderloins and slice into bite sized pieces.
In a frying pan, place the mushroom, onion, green beans, bell pepper, and the chicken tenderloins. Pour 2 tbsp of water and cover with lid.
Place the frying pan over the stove top and turn on the heat to medium. Cook for 2 to 3 minutes. With this method, the umami and juice of vegetables are well induced. (This technique is called “Kasaneni” in Japanese.)
Open the lid and place the noodles then cover with the lid again. (If the water is already evaporated, add 2 tbsp of water.) Cook for another 1 minute.
Open the lid and sprinkle with the soup base. Mix well.
Pour the olive oil and mix well. Transfer to the serving plate.
Serve the Yakisoba with mustard mayonnaise, roasted sesame seeds and spring onion.