In a large mixing bowl, combine the diced salmon and tuna with ½ tbsp soy sauce, ¼-½ tsp truffle oil, 1/2 tbsp olive oil, and 1 tbsp scallions. Mix until well combined. Place in the fridge to marinate while prepping the remaining recipe.
In a small bowl, combine ¼ cup mayonnaise with 1 teaspoon of yuzu or lemon juice and ½ teaspoon of sriracha. Mix until fully combined. Taste and add salt or yuzu juice as needed.
To serve, place 3-4 scoops of the yuzu mayo mixture onto a plate or bowl. Then, gently place a few scoops of the marinated tuna and salmon on top of the mayonnaise. Garnish with a small pinch of black sesame seeds, and serve with crispy nori chips to the side.