*If you have the time, marinate your beef in some soy sauce and sesame oil. I marinated the meat in the morning before I left for work so the meat was marinating all day. Marinating the meat just makes it taste so much better.
Get all of your vegetables cut and ready to go
Boil the spinach just for 2-3 minutes, rinse, chop up and set aside
In a large pan or wok over medium heat, heat vegetable (or olive) oil and 1 Tbsp sesame oil.
Add onion slices and garlic and sauté for about 1 minute.
Add the rest of vegetables and cook for 4-6 minutes, until the vegetables are half-cooked and still a bit crispy.
In a separate pan, cook the beef. I prefer to do this separately to ensure all the meat gets cooked evenly.
Cook noodles according to package directions. (usually 4-5 minutes)
Turn heat to low and add cooked noodles, meat (if using), soy sauce, sugar, and the remaining sesame oil. Mix to combine and cook for another 2-4 minutes.
Add salt or more soy sauce if needed; you can also look at the color of the noodles to see if more soy sauce is needed. Taste. If using sesame seeds, sprinkle them on top, serve and enjoy!