In a small bowl, whisk together the lo mein sauce ingredients. Set aside.
In another bowl, mix the lo mein meat marinade ingredients together and set in the fridge for at least 30 mins.
Cook the lo mein egg noodles according to the package instructions until al dente. Drain and set aside.
In a skillet, add the sliced onion, bell pepper, carrot, cabbage, and mushrooms to the skillet. Stir-fry for 3-4 minutes until the vegetables are tender-crisp.
In a separate large skillet or wok, heat the vegetable oil over medium-high heat. Add the minced garlic and cook for about 30 seconds until fragrant.
Add beef to the large skillet and add the vegetables to it and toss until heated through.
Add the cooked noodles to the skillet. Set the noodles to one side of the pan and pour the sauce mixture to the other side and let it simmer a bit. Toss everything together until the noodles are evenly coated with the sauce and heated through. Season with salt and pepper to taste.
Add some sliced green onions at the end for garnish!