Open the oysters: hold the oyster in one hand in a kitchen cloth, rounded side down and insert the point of an oyster knife next to the hinge. Twist to open and slide the knife along inside the top shell to release the muscle attaching the oyster to the shell. Remove the top shell then loosen the oyster from the bottom shell
Remove the oysters from their shells and drain on kitchen paper.
Heat the olive oil in a frying pan and cook the oysters for about 1-2 minutes, so that they stew rather than fry. Sprinkle with lemon juice and season with pepper.
Remove from the pan. Place an oyster on each baguette slice, scatter with diced tomatoes and garnish each with lemon zest.