Add half a yellow onion sliced, 2 tbsp gochujang, 2 tbsp gochugaru, 1 tbsp soy sauce, 1 tbsp chicken bouillon powder, 1 tbsp sesame oil, 3 cloves grated garlic, a knob of grated ginger, 1 tbsp white sugar, 1 tbsp water, cooking oil, and black pepper to a large bowl.
Add the cubed chicken thighs to the bowl and mix to coat in the marinade.
Heat a cast iron or oven-safe pan over medium-low heat and add the marinated chicken. Simmer for about 25 minutes until the chicken is cooked through.
Turn on the broiler. Sprinkle shredded mozzarella cheese over the chicken and broil until the cheese is melted and bubbly.
Remove from the oven and top with sliced green onions.
Serve with rice, lettuce wraps, or corn tortillas.
