Place the cumin seeds, Sichuan peppercorns, white peppercorn, fennel and coriander seed into a coffee grinder and blitz until you obtain a fine powder.
Dump the mixture into a small bowl and set aside.
Marinate the lamb meat:
In a large bowl, place the sliced lamb, 1 teaspoon cornstarch, ¼ teaspoon salt, 1 tablespoon soy sauce, and 2 tablespoon of the ground cumin powder mixture from above.
Mix the meat thoroughly. Cover and place in the fridge to marinate for 2 hours (for maximum flavour). If you don't have time, marinate the meat for a minimum of 20 minutes.
Cook the noodles:
Fill a large pot with water and bring to a boil.
Add in the thick-cut noodles and cook according to the package directions, about 2-3 minutes.
Drain the noodles and set aside.
Make the sauce:
In a bowl, combine the soy sauce, salt, sesame oil and black vinegar. Give it a stir and set aside.
Stir-fry the noodles:
Heat a wok or large pan with 1 tablespoon avocado oil. Add in the minced garlic, green onion and sauté until fragrant, about 1 minute.
Next, add in the sliced marinated lamb and cook, stirring constantly for about 3-4 minutes.
Add in the red onions, bean sprouts and Serrano chili and sauté for another minute before adding the noodles.
Pour in the soy sauce mixture. Use a pair of tongs to coat all the noodles with the sauce.
Remove from heat, add a heaping spoonful of chili oil and garnish with chopped cilantro and green onion. Sprinkle with additional ground cumin mixture if desired.