Halve, pit, and thinly slice the avocado. Halve the lime. Squeeze the juice of half the lime over the avocado to prevent browning.
In small bowl, whisk together the mayonnaise, a squeeze of lime juice, and the wasabi paste (to taste).Thin to a dressing-like consistency with 1-2 tablespoons water, then season with salt and pepper.
Plate the ahi tuna on the mixed greens with the avocado on the side. Sprinkle with the sesame seeds, togarashi and drizzle with wasabi-lime dressing.