In a bowl, add the kimchi and chop it into small pieces (cutting directly in the bowl prevents staining your cutting board).

Add the drained tuna, diced celery, Kewpie mayo, and gochujang. Mix well.

Heat a pan over medium heat and add butter.

Place one slice of bread in the pan, then layer with the tuna mixture and a generous amount of mozzarella cheese. Top with the second slice of bread.

Toast until golden brown, then flip and toast the other side until crispy and the cheese is melted.

Remove from the pan, cut in half, and enjoy!