Combine sesame seeds and togarashi on a tray. Roll tuna in sesame mixture, pressing lightly to form a crust.
Heat 1 tbsp peanut oil in a large frying pan over high heat. Add tuna and cook on each side until just seared (15-20 seconds each side). Cool, wrap in plastic wrap and refrigerate until firm (45-50 minutes).
Combine cucumber, carrot and coriander in a bowl and set aside.
Whisk soy sauce, vinegar, sesame oil, mirin, wasabi and remaining peanut oil in a bowl, season to taste, drizzle 60ml over salad and toss to combine.
Arrange in small piles on a platter. Slice tuna 7mm thick, remove plastic wrap, arrange over salad, drizzle with remaining dressing and serve.
