Just leave some in the bottom of the packet and gently mash with a rolling pin or similar on a chopping board. You want crumbs about the size of panko.

I think some of the taste if you just ate the chip by itself gets lost in the cooking, but it gives a bit more flavour than ordinary panko. You can probably achieve exactly the same thing, and a bit easier, by adding off-the-shelf lemon pepper or other spices of your choice to panko crumbs in a little bowl before the cooking process.