Prepare the Tuna: Pat tuna steaks dry with paper towels. Season both sides with salt and pepper.
Coat with Sesame Seeds: Mix black and white sesame seeds on a plate. Press each tuna steak into the seeds to coat both sides evenly.
Heat the Pan: Heat sesame oil and olive oil over medium-high heat until shimmering.
Sear the Tuna: Add the tuna steaks and sear for 45–60 seconds per side for rare, or up to 2 minutes for medium-rare.
Make the Sauce: In a small bowl, whisk together soy sauce, rice vinegar, wasabi paste, sesame oil, and honey until smooth. Add green onions if desired.
Slice and Serve: Remove tuna from the pan and let rest for 1–2 minutes. Slice thinly against the grain and serve with the dipping sauce.