Mix all seasoning ingredients together in a small bowl.
Add the beef and mushrooms together in a bowl, and mix in about 2 1/2 tbsp of seasoning to marinate the ingredients. Set aside.
Prepare the sweet potato noodles according to package instructions, about 6-7 minutes. Rinse, drain, cut the noodles to about 6-7 inch lengths, and set aside.
In a lightly oiled skillet on medium heat, add the onion and green onion. Add a pinch of salt and cook for about 1-2 minutes until aromatic. Remove and set aside.
In the same skillet, add a little more oil and add the carrots and red bell pepper. Lightly season with salt and cook for about 1-2 minutes, ensuring the vegetables are still crisp. Remove and set aside.
Lightly oil the skillet and reduce the heat to medium-low. Add the beaten eggs into a thin omelet, and flip when the bottom is cooked. Transfer to a cutting board, let it cool slightly, and cut into thin strips.
In the same skillet, add the marinated beef and mushrooms and cook until the meat is cooked through, about 2-3 minutes. Transfer back into the bowl.
Lightly blanch the spinach by adding them to a pot of boiling water for about 30 seconds. Rinse and squeeze out any excess water. Lightly season with salt and pepper (and garlic, if preferred), and cut into bite-sized pieces.
In a lightly oiled skillet on medium heat, add the rest of the seasoning and the prepared noodles. Mix well and stir around until the noodles are evenly coated with the sauce. When the sauce is absorbed into the noodles, remove from heat and transfer into a large mixing bowl.
Mix in the prepared onion, green onion, spinach, carrot, red bell pepper, beef, mushroom, and eggs into the noodles, and mix thoroughly until all ingredients are evenly combined. Garnish with toasted sesame seeds, adding more soy sauce and/or sesame oil to preference. Serve warm and enjoy!