This dressing can be prepared earlier and chill in the fridge.
Deseed the chillis, add in a blender along with cucumber, onions, coriander, lime and olive oil. Blitz for a few seconds so its just roughly chopped. Put in a bowl and season to taste.
Clean the oysters under running cold water, I would advise using a brush to get rid of all the grit and dirt. Hold the oyster with a tea towel with the hinge side sticking out. This is just a precaution, just in case the knife slips.
With the flat side of the oyster facing upwards, insert the oyster knife in the hinge, slowly edge the knife inside, taking care that the shell do not break.
I would strongly advise to use an oyster knife to do this, NOT a regular knife.
When the knife has penetrated the hinge, slowly give the knife a twist to separate the shells, keeping the blade close to the top flat shell, slide it in along to cut the muscle holding the two shells together.
Once the oyster is open, slide the knide underneath to cut the muscle from the shell. The flip the oyster, be careful not to spill any of the juices.
Arrange the oysters in a large plate, then spoon the dressing on top.