Junction box in dishwasher bay
Use a Non-Metallic (NM) splice kit; these are allowed in a wall without a box, as per NEC 334.40(b). These run about $15.00, maybe more.
 A box can be accessible behind a panel designed to be removable, but a dishwasher would not meet that requirement for accessibility. 

Added : tyco non metallic splice , 2 wire non metallic splice, 3 wire non metallic splice will all bring up the models available 14-21$ from what I saw today. I have a few, just in case I cut a cable in a wall.  I have no association with any of the mfg’s it is a product that has saved me time and $.