Spread mayonnaise on one side of each of the slices of bread.
Mix the cheeses together and set aside 1/3 cup of it in a small bowl. Mix the remaining cheese with the spring onion and a grind of black pepper. Spread the plain side of the bread slices with chili jam and then sprinkle with the cheese and spring onion mix. Top with the other slice of bread, mayonnaise side facing out again.
Heat a frying pan over medium heat and place half of the butter into the pan followed by the sandwich. Sprinkle over half of the cheese you set aside and cook for 2 minutes. Flip over, slide in the remaining butter and sprinkle with the remaining cheese. Cook for another 2 minutes on the other side. Flip again and cook for 2 minutes then flip again and cook for another 2 minutes until golden.