With a paring knife, remove the skin from the outside of the cucumber. Coarsely chop the skin. Discard the remaining cucumber or reserve for another use. In a blender, puree the cucumber, parsley, and vinegar and season with salt and pepper. Add the egg yolks and sugar and blend for 30 seconds to combine. With the blender running, add the oils in a slow steady stream to form an emulsion. Season, to taste. Refrigerate until ready to use.
Season the scallops with salt and pepper and set aside. Place the curry powder in a small saute pan and heat over medium heat, stirring constantly. Cook for 30 seconds or just until you can really smell the curry. Immediately remove from the pan and place in a shallow bowl or plate. Add the flour and mix well. Dredge the scallops in the curry mixture, shaking off any excess. Set aside on a clean plate.
Heat a large saute pan over high heat. When the pan is hot, add the peanut oil and heat just to smoking. Add the scallops and saute for 30 seconds. Turn the scallops and add the butter and saute for an additional 30 seconds on the second side. Remove from the pan to a paper towel-lined plate.
Place a small pile of watercress on 6 plates. Top the watercress with a scallop shell. Place some sauce in each scallop shell. Top with 1 scallop. Garnish with 1 tablespoon salmon caviar and chive flowers.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.