Fill voids in a butcher block
If you can, I would recommend cutting down the joint with a thin bandsaw blade &amp; then machining both pieces with a jointer to get the super tight fit that you really should have between your boards.  The reason I suggest this is that cutting boards can give up particles when sliced/chopped on that would end up on the food that is processed on the cutting board (especially meat)--which I doubt you or anyone else would want to eat, due to the toxicity of adhesives.

If, on the other hand, you can find a non-toxic bonding adhesive then the above suggestion could be avoided.

hth
best regards!