If you want to prepare kimbap the night before and refrigerate it to eat the next day, the best way to heat it is by frying: dip the whole (uncut) rolls in beaten egg, then dredge in panko ...

You can take that even further by either giving it an egg wash before ... Then, if you want to dip them in something, gochujang, spicy mayo, or soy sauce pair well, but these kimbap are plenty ...