In a large pot of salted boiling water, cook the noodles according to their package directions. Drain and set aside.
For the sauce:
Combine the bouillon, oyster sauce, soy sauce, sesame oil and Sriracha in a large glass measuring cup or small bowl and set aside. This may look like a lot of sauce, but you have a lot of noodles and veggies to coat!
For the lo mein:
Heat a wok over high heat. When hot, add 1 tablespoon vegetable oil, half the garlic, half the ginger and half the scallions and saute 30 seconds. Add in the shrimp and cook until they just start to turn pink and curl up, about 2 minutes. Transfer the shrimp and aromatics to a plate and reserve.
In the same pan, heat the remaining 1 tablespoon vegetable oil and add the remaining garlic, ginger and scallions. Saute 30 seconds, and then add in the mushrooms, celery, carrots and cabbage. Saute the veggies until they begin to brown and caramelize, 4 to 5 minutes.
Whisk the cornstarch into 2 tablespoons cold water. Once dissolved, add to the sauce. Add the sauce to the pan with the vegetables and bring to a simmer. Toss in the reserved shrimp, aromatics and noodles and serve!