To prepare each fillet, center it on a short end of a sheet of parchment, a few inches from the edge. Top it with one quarter of the pesto-veggie mixture. Fold the parchment in half over the fish. Fold in a corner of the creased edge to seal it. Working around the perimeter of the packet, make another overlapping fold, then continue in this manner, overlapping as you go, until the packet is completely sealed.