Marinate the Chicken: In a mixing bowl, combine the boneless chicken thighs with gochugaru, minced garlic, black pepper, gochujang, soy sauce, and your choice of sweetener. Massage the marinade into the chicken for about 2-3 minutes until all pieces are thoroughly coated. Let it marinate while you prepare the noodles.

Cook the Noodles: Bring a large pot of water to a rolling boil and add the noodles, cooking them for about 3-4 minutes until they are slightly undercooked but still chewy. Drain the noodles in a colander and rinse them briefly under cold water to stop the cooking process. Set the noodles aside.

Fry the Chicken: In a large non-stick skillet, heat 2 tablespoons of neutral oil over medium-high heat. Once the oil is shimmering, add the marinated chicken in a single layer and cook for 2-3 minutes per side, or until golden brown but not fully cooked through.

Prepare the Vegetables: Transfer the browned chicken to a plate and cut into bite-sized pieces. Push the chicken to the edges of the skillet, making space for the sliced onion and mushrooms. Sauté the vegetables for about 3-4 minutes until the onions are translucent and the mushrooms are softened.

Combine and Finish: Add the cooked noodles to the pan with chicken and veggies. Toss everything together for around 2-3 minutes, ensuring the noodles absorb the spices and sauce. Sprinkle shredded cheese generously on top, allowing it to melt over the hot noodles.