Preheat oven to 400 degrees F, then cut four 15" rounds of parchment paper. Fold each in half, then unfold & lightly brush 1/2 tsp oil onto each parchment round to within 1" of the edge.
Arrange potato slices evenly on half of each parchment round, & sprinkle with half of the salt & pepper.
Put salmon on top of that, & sprinkle the remaining salt & pepper, before doing a final top-off with the carrots, tomatoes & 2 herb sprigs.
To seal each packet, fold untopped side of parchment round over the topped side. Fold open edge over several times, folding & twisting until packet is completely sealed. Place packets on ungreased cookie sheet.
Bake in oven for 15-20 minutes, depending on the thickness of the filets. Carefully unwrap 1 packet to check if fish flakes easily with fork. If not done, re-wrap & continue baking.
Remove packets from oven & let stand 5 minutes before serving.
Place packets on individual serving plates, then cut an X-shaped slit in the top of each packet. Carefully tear back the paper to serve.