For the Basil Mousseline
Pulse mayonnaise with basil and green onion in a food processor and scrape into a bowl. In a separate bowl, whip cream to soft peaks and stir in lemon juice.
Fold cream gently into mayonnaise and season to taste. Chill until ready to serve. (Mousseline can be prepared up to 6 hours in advance).
For the Poached salmon
Preheat oven to 135°C. In a flat-bottomed roasting pan and sauteuse (sauté pan with tall sides), bring wine, water, lemons, onions and oregano or dill up to a simmer.
Turn off heat and add salmon portions. Cover pan or dish and place in oven. Cook for 15 to 20 minutes, checking temperature/texture at 15 minutes.
To check doneness, salmon should be an internal temperature of 60°C and flesh should feel firm when gently pressed.
Remove salmon from liquid gently using a slotted spoon and place onto a plate. Season salmon lightly. Cool to room temperature, then chill completely.
To serve, peel away skin of salmon and place on plate or platter. Top with mousseline and sprinkle with red pepper. Serve cold.