Make a deep slit on the king prawns. In a bowl, take some butter and add chopped garlic, salt and crushed black pepper. Next add the slit king prawns and mix well. Heat a grill pan and place the prawns for grilling. Grill both sides well. For the sauce, heat butter in a pan. Add chopped garlic chopped spring onion greens, mixed bell pepper juliennes and cook them. Transfer the grilled prawns to a serving plate and top them with the prepared sauce. Serve hot.