Top each fillet with 3 tomato slices, one quarter of olives, 1/8 teaspoon red pepper flakes, one quarter each of butter and zest, and 1 herb sprig.
Working with one package at a time, fold left half of parchment over fillet.
Starting at one corner of crease, fold edge of parchment over in triangles (each fold should overlap previous one), following a semicircular path around fillet, smoothing out folds as you go and tucking last fold under to seal papillote completely.Heat a large baking sheet in oven for 5 minutes.
Put papillotes on hot baking sheet and bake for 9 minutes.To serve, transfer packets to four plates; with a knife, slit top of each packet and tear it to expose fish (use caution: steam will escape).
Slide fish and sauce onto plates and discard paper.