Cut the Bonito into eight 1/2 inch thick steaks (Bonito is strong). Mix the Balsamic and mustard place it and the steaks into a zip lock bag to marinate for 15 minutes. Use half the mayo to coat the bottom of the cooking board (the slight Cedar flavor is wonderful)
Place the bonito steaks on the cooking board. Slather the remaining Mayo on top of the steaks. Mince the onion and place on the steaks. Mix the brown sugar and the bread crumbs together and coat the top and side of the Bonito (bread crumbs in a blender adding the brown sugar a little at a time works great). Spread the chease over the breading. Bake in a 275 degree oven for 20 to 25 minutes
Serve board discard the Bonito. Serve while still warm.