Peel the ginger and garlic. Remove the germ from the garlic and slice it, along with the ginger, into very fine strips, then cut into tiny cubes. Set aside in a bowl.
Add the oil and vinegar and season to taste. Lay the herring fillets flat on a large platter and coat with the vinaigrette. Leave to marinate for at least 2 h.
Dice the herring fillets and arrange them on the gluten-free sigdal oat crackers. Add a teaspoon of the marinade, garnish with a few sprigs of dill and a teaspoon of Tobiko eggs.