Leaf Miner

This damage appears to be caused by a leaf miner. A small fly or moth lays its eggs beneath the surface of the leaf and when the eggs hatch, the larvae tunnel thru the leaf tissue, consuming the nutrients in the foliage. Once the damage has been done, nothing will reverse it. Chemical pesticides are not effective against this pest because most products won’t penetrate thru the leaf surface although organic products containing Spinosad have often worked to prevent further infestation. Once the damage has been done to the leaf, it is not reversible. Usually the damage done by these insects is not going to kill the plant unless the infestation is extensive. Here is a link that you might find helpful: http://www.ipm.ucdavis.edu/PMG/GARDEN/VEGES/PESTS/vegleafminers.html