Cut the chives to 5cm widths and thinly slice the onions. Remove the root/bottom of the shimeji mushrooms and separate the mushrooms.
In a separate bowl, mix the egg well. Stir fry the eggs and set aside.
Mix together the soup seasoning, oyster sauce, fish sauce, lemon juice, and sugar. Set aside.
Add plenty of water to a pot bring to a boil. Add the udon noodles and cook for 2 minutes. Rinse and drain the noodles, making sure to get rid of the water. Set aside.
Heat oil in a frying pan and add in the onions, mushrooms, and shrimps. Cook thoroughly. After cooking the shrimps, add in the udon noodles, chives, bean sprouts, and stir-fried eggs. Stir in the sauce from Step 3 and continue to stir-fry the noodles, until the sauce is well mixed with the noodles.
Place the noodles on a plate and finish by adding a slice of lemon. Enjoy!