Slice the fish into 8 same-size pieces. Cut 8 pieces of parchment paper, slightly larger than the salad plates. (If you have round cake pan liners, they work perfectly for this).
Brush a piece of parchment with oil and place 2 of the salmon slices side by side in the center of the paper, flat side abutting each other. Brush another piece of parchment with oil and put it on top of the salmon. Make 3 more parchment-salmon “sandwiches” with the rest of the salmon. Put them all in the refrigerator to stay cold.
Take one out of the refrigerator and use a meat pounder, a mallet and wide metal spatula, or the flat bottom of a frying pan to gently pound out the salmon round and thin. Pound with a downward and outward motion, forming the fish into a flat disk. Rotate the parchment as you pound and lift it to the light now and then to see whether the salmon is being flattened evenly. Make the circle of fish just smaller than the chilled plate. Repeat with all the pieces. Keep refrigerated until ready to serve.
Remove the seeds from a mature cilantro flower head. Pound slightly with a mortar and pestle.
Remove the blossom from a few sprigs of flowering herbs (such as chervil, cilantro, thyme, borage, rosemary, sage, or nasturtium).
When ready to serve, carefully peel the top sheet of parchment away from the fish and invert onto a cold plate. Peel off the other piece of paper. Season with salt and pepper. Squeeze lemon juice over and drizzle with olive oil. Scatter the crushed coriander and herb blossoms over and serve immediately.