1. In a small bowl, add all the seasoning ingredients and mix well. Set aside.
2. Cook the spinach in boiling water (for a few seconds) and cool it down with cold tap water. Squeeze the spinach to remove excess water and mix with 1/4 tsp salt and dash of pepper. Cut roughly if you like and set aside.
3. In another bowl, add the beef and soak with 2 tbsp seasoning mixture from #1. Set aside.
4. In a frying-pan, heat 1 tbsp sesame oil, add the beef and 1/2 tbsp garlic powder. Cook until the beef is no longer pink. Transfer to the plate and set aside.
5. Using the same frying-pan (as is, without washing) heat 1 tsp sesame oil (or vegetable oil) and fry carrot lightly or until wilted according to your taste. Do the same separately for onion, mushroom and red bell pepper, adding 1 tsp sesame oil or vegetable oil each time.
6. Heat 1 tsp oil in another frying pan over medium heat. Pour beaten eggs to the pan and swirl the pan to cover the surface of the pan in a thin layer. Cook until just set, then flip over and cook for a few seconds. Transfer the egg to a plate to let cool. When its cooled, roll up and cut into thin ribbons. Set aside.
7. Boil Korean noodles according to package directions or 6 to 7 minutes. Wash with cold water and drain well.
8. In a large wok, heat 1 tbsp oil and place the cooked noodles. Pour the seasoning sauce from #1 over the noodle. Fry gently to warm it up over low heat for a few minutes. Add all the cooked beef and vegetable (carrot, onion, mushroom, leek, spinach and paprika) and stir well.
9. Transfer to a serving plate and garnish Japchae with the eggs and sprinkle some white sesame over it.