Grill the fish on a gas burner or in a grill pan until you have a good crust. Put the fish aside. Make the ponzu sauce by mixing the hoisin sauce, soy sauce, yuzu juice, sugar, rice vinegar, ginger, green chilli and garlic. Find the right sweet and sour balance to taste. Make a salad of seaweed, cucumber and fennel and add the mirin, yuzu juice and sesame oil to taste. Whip the egg with lemon juice and salt. Gently add the oil for a creamy mayonnaise. Add the sriracha to taste. Brush the fish with ponzu sauce and cover in sesame seeds. Finely slice the fish and serve the salad and mayonnaise on the side. Sprinkle with chopped coriander and fennel fronds.