1. Loosen oysters from their shells and rinse shells to remove any grit. Replace oysters on the shell and season with salt and pepper. Chill until ready to serve.
2. Coarsely grate cucumber and combine with sesame oil and lemon juice. Toss well and place a small amount on top of each oyster, then scatter with a few sesame seeds.
3. Serve chilled oysters on a bed of rock salt, with lemon wedges on the side to squeeze over.

Tip: To serve oysters in the shell, place a mound of rock salt on a serving platter and arrange the oyster shells on top (the salt will hold the oyster shells in place).