In a medium bowl, combine cubed chicken, garlic powder, salt, pepper, fish sauce, and freshly grated ginger. Stir until each chicken piece is evenly coated. Marinate briefly while you prepare other ingredients to enhance flavors.

Step 2: Cook the Noodles

Bring a pot of water to boil and add buckwheat lo mein noodles. Cook according to package instructions, undercooking by 1–2 minutes for optimal texture. Drain noodles thoroughly and set aside.

Step 3: Sauté the Chicken

Heat 1 tablespoon cooking oil in a skillet or wok over medium-high heat. Add marinated chicken pieces, cooking until golden brown and fully cooked through (about 6–8 minutes). In the last 2 minutes, add 1 tablespoon Szechuan garlic butter and half of the minced garlic, sautéing until fragrant. Transfer cooked chicken to a plate and keep warm.

Step 4: Sauté the Vegetables

In the same skillet or wok, add another tablespoon of cooking oil if needed. Toss in remaining minced garlic and grated ginger, sautéing for approximately 1 minute until aromatic. Add cabbage, carrots, green onions, mushrooms, broccoli, and celery, stir-frying until tender-crisp, approximately 5–7 minutes.

Step 5: Combine and Sauce

Return the cooked chicken to the pan containing vegetables. Add the undercooked noodles along with soy sauce, hoisin sauce, fish sauce, black pepper, and remaining tablespoon of Szechuan garlic butter. Mix thoroughly over medium heat until noodles finish cooking and all ingredients are coated evenly with sauce, about 2–3 minutes.