In a mixing bowl, combine the gochujang, gochugaru, sugar, soy sauce, salt, pepper, ginger and garlic. Add the chicken to this mixture and mix evenly. Leave it aside for 15 minutes
Heat a skillet with the oil and add the marinated chicken along with ¼ cup water. Mix well, cover and cook, on medium heat, for 20 minutes or until the chicken is cooked
Remove from flame and top the chicken with the mozzarella. In case your skillet/cooking pan is not oven proof* transfer the chicken to a baking dish, cover with the cheese and proceed to next step
Place the pan/dish in the oven, under broiler, until the cheese has fully melted and browned in a few spots (about 2 minutes)
Remove, garnish with spring onion greens and serve your mouthwatering Korean fire chicken (cheese buldak) hot, as is or with steamed rice. Enjoy!