Wash the tuna, dab dry and cut into small cubes (approx. 7 mm). Halve avocados, remove seeds. Remove the flesh from the skin and also dice. Season fish and avocado with salt and pepper.
Lightly roast sesame seeds in a pan without fat. Wash the chives and cut into small rolls. Peel and finely grate the ginger. Mix mayonnaise, soy sauce, orange juice, sesame oil and wasabi with a whisk, stir in ginger.
Carefully fold the fish, avocado, sesame and chives into the dressing.