Add baking soda, cornstarch, soy sauce and mirin to a large ziplock bag.
Add strips of flank steak to the bag.
Toss well to coat the beef, then place in the refrigerator for 30-60 minutes.
Stir Fry Sauce
Prepare the sauce by whisking all of the ingredients together in a small bowl. Set aside.
Stir Fry
Once the steak has tenderized for 30-60 minutes in the refrigerator, remove it from the fridge.
Bring a large pot of water to boil on the stove.
Add the lo mein noodles to the boiling water and cook for 4 minutes.
Drain and set aside.
While the noodles are cooking, add the canola oil to a large skillet or wok on the stove over high heat.
Remove the steak from the marinade, shake off any additional marinade, then add the steak to the skillet.
Cook for 2-3 minutes.
Remove the steak from the skillet and set aside.
Add the onion, bell pepper, asparagus and garlic, stir fry for 3-4 minutes.
Add the beef back to the skillet, along with the cooked lo mein noodles and sauce.
Toss to combine everything, remove from the heat and top with the sesame seeds and diced green onions.
Notes
Gluten Free Option: Use gluten free soy sauce and gluten free hoisin sauce in the marinade and stir fry sauce. Substitute the lo mein noodles with rice noodles or gluten free spaghetti noodles.
Slicing The Steak: slice the steak against the grain, meaning, in the opposite direction of the white lines running through the steak. Slice into 1/4 inch thick slices.