For the dressing, mix together the sesame oil, soy sauce, sherry vinegar, honey and ginger; set aside. Heat a griddle pan over a high heat.
Brush the tuna steaks with the olive oil and season; griddle for 1-2 minutes on each side until the juices run clear, then set aside.
Pare long strips of carrot using a vegetable peeler and toss with the spinach and half the dressing. Divide between 2 plates. Top with the tuna, then scatter over the pistachios and sesame seeds. Drizzle with the remaining dressing before serving.
Dry toast the pistachios and sesame seeds separately in a frying pan. Toast extra and store in airtight containers for sprinkling over salads, noodles and rice dishes.