In a large high-sided skillet, add the water and bring to a simmer.
Gradually whisk in the matcha powder, followed by 1 teaspoon salt, followed by the cream. Reduce the heat to low and let the temperature of the liquid sink below 180°.
Slide in the salmon fillets, skin sides up. Turn off the heat. Depending on the thickness, let the fillets poach for 10 minutes.
Sacrifice the perfection of one of the fillets. Using a spoon, try to make a clean break at one of the flakes. If the salmon still has a tint of translucency in its flake, it's done.
Transfer to a plate. (That tester is your piece, by the way.) Put the fillets somewhere warm, like in a oven with a pilot light, or on the plate over the warm liquid (providing the plate's diameter is wide enough).
In a small skillet, add the grapeseed oil. Turn the heat to medium. Add the ginger. Yes, now.
As the grapeseed oil warms, you'll start to smell the sweet essence of cooked ginger. Stir constantly.
Now, add the crumbs, and raise the heat to medium-high.
Tumble the crumbs while shaking the pan, popcorn-style, until well toasted. Remove the pan from the heat and stir in the lime zest.
Arrange the fillets on plates or a platter, skin sides down; sprinkle with 1/4 teaspoon salt.
Now, lightly brush the salmon fillets with the mayonnaise, and sprinkle the toasted crumbs in an even blanket on top of the fillets.
Garnish with chives. Serve with lime wedges.