Cut the tuna into cubes for the Poisson cru au lait de coco and cut a plate of sliced tuna shoulder for the sashimi.
Place the cubes of tuna in a bowl of sea water to soak. While the fish is soaking, finely cut the onion and the carrot and set aside. Drain the fish from the sea water (after 5-10 minutes) and squeeze out any remaining water. Place in bowl with onion and carrot. Add coconut cream and salt and pepper to taste and mix.
For the Tahitian Sashimi Sauce add 2 teaspoons of oyster sauce to a mixing bowl, add 1 teaspoon of soy sauce 2 teaspoons of mustard, two cloves of garlic and one tablespoon of canola oil. Hand mix till smooth. Finish with juice of a lime.