1. Make fried onion Add the sliced onion, garlic and oil in a microwaveable bowl and microwave them, uncovered, for 5 minutes (at 600W). Remove and gently stir. Microwave for 3 minutes again and stir gently. Now repeat again but once the onion starts changing to light brown color, check them every minute and stir every time. We want them exactly crispy and evenly colored :-) So stop heating when you get there. Drain excess oil on a pepper towel and set aside.
2. Make the soup In a medium bowl, add the ingredient "A" (garlic, sesame oil, salt) and set aside. That's our marinade. In a large pot, heat 1 tbsp oil and fry the ingredient B (ginger and garlic) until fragrant. Add the water and beef, then bring it to a boil. When the beef is no longer pink, take it out of the water (do not throw away the water!) and put it to soak in the marinade bowl. Set aside.
3. Add the soup ingredients to the water (the one in which you boiled the beef) to season the soup.
4. Bring a large pot of lightly salted water to a boil and then cook the rice noodles in the boiling water until soft. It should take about 1 minute, do not over cook.
5. Divide the noodles into 5 serving bowls, top with beef and ladle the hot soup over the noodle. Then top with bean sprouts, fried onion and green chili pepper (optional) to serve.