Finely grate the ginger, then wrap it in a piece of muslin or a clean kitchen towel. Squeeze out the juice into a small bowl and set aside.
In another bowl, whisk the egg yolks with the salt and 1 teaspoon of lime juice.
While whisking continuously, add the sunflower oil drop by drop until the mixture begins to emulsify. Once it thickens, drizzle in the remaining oil gradually.
Stir in the wasabi powder, ginger juice, and the rest of the lime juice. Taste and adjust seasoning, adding more wasabi or lime juice if desired.
Chill until ready to serve.
This homemade wasabi mayonnaise keeps for 2–3 days in the fridge.