Shuck the oysters by removing the oyster shells, making sure you leave in the oyster liquor. This can be quite a difficult task. Hold the oyster, flat side down, in a tea towel. Locate the hinge (at the more pointed end). Insert a flat knife, screwdriver or oyster knife in between the shells and near to the hinge, then twist. It should pop open. Reserve the domed shell half, clean and dry thoroughly; you will use these for a service vehicle.
Prepare the wasabi mayonnaise by first mixing a little of the mayonnaise with the wasabi paste to ensure there are no lumps. Next stir in the remaining mayo – you can add a little more wasabi to taste depending on preference.
Shred the red chilli and spring onion as fine as possible and leave in ice cold water to crisp. Heat the oil for deep frying to 200ºC. You'll know it's ready when a cube of bread dropped into the oil turns golden brown within 40 seconds.
To prepare the batter, sieve the flour with a pinch of fine salt into a bowl, add ¾ of the soda water and whisk until well incorporated. Try not to overwork it, you are looking for the consistency of double cream. Add a little more water if required.
Remove the oysters carefully out of the reserved liquor, shaking off the excess. Dip oysters in the tempura batter and fry quickly for 1-2 minutes until beautifully crisp and golden brown. Drain on paper towel and season with a pinch of salt.
Spoon, or better still pipe, some wasabi mayonnaise onto the oyster, and then sprinkle on a few shredded pieces of chilli, spring onion, chives and a little fresh lime zest with a micro plane. Place the oysters back in the shell and enjoy immediately.