Heat the butter in a large frying pan or skillet over medium-high heat. Once melted, add the diced Spam and cook for 3–4 minutes, stirring occasionally, until golden and crispy around the edges.
Add the diced onion and garlic, then cook for 2–3 minutes until softened and fragrant. Stir in the chopped kimchi and gochujang, cooking for another minute until the gochujang has dissolved and evenly coated the kimchi.
Add the day-old cooked short-grain rice, breaking up any clumps with your spatula. Stir until the rice is evenly coated with the kimchi and Spam mixture.
Pour in the soy sauce, sesame oil and sugar, stirring well to combine. Mix through the sliced spring onions and cook for another minute.
Remove the pan from the heat and sprinkle the grated mozzarella evenly over the top. Melt the cheese using a blow torch, or place the pan under a preheated grill (broiler) for around 5 minutes until melted and bubbling.
Divide between bowls and top with a fried egg, extra spring onions and seasoned roasted crushed laver, if desired. Serve immediately.