In a mixing bowl, combine the boneless chicken thighs with gochugaru, minced garlic, black pepper, gochujang, soy sauce, and sweetener. Massage the marinade into the chicken thoroughly and allow to marinate for at least 10 minutes.

Bring a large pot of salted water to a boil and add the noodles. Cook according to package instructions for around 4-5 minutes. Drain the noodles and set aside.

Heat a tablespoon of neutral oil in a non-stick skillet over medium-high heat. Add the marinated chicken thighs and cook for about 2-3 minutes on each side until golden brown and cooked through.

Once the chicken is nearly cooked, slice it into bite-sized pieces and push to one side of the pan.

Add the sliced onion and mixed mushrooms to the pan, sauté for 3-5 minutes until onions are translucent.

Introduce the cooked noodles into the skillet, tossing everything together gently for another 2-3 minutes to soak up flavors.

Sprinkle the shredded cheese over the top, cover with a lid, and cook on low heat for about 2 minutes until cheese melts.