Prepare the Marinade - whisk together olive oil, sesame oil, ground ginger, soy sauce, garlic powder, rice vinegar, and half of the sesame seeds in a small mixing bowl.

Marinate the Tuna - place tuna steaks in a dish and cover with half of the marinade. Seal and refrigerate for at least 20 minutes.

Preheat the Grill - set your grill to medium-high heat, around 350°F, or heat a skillet with olive oil for pan-searing.

Coat the Tuna - remove steaks from the fridge, discard excess marinade, and coat each steak with reserved sesame seeds.

Grill the Tuna - cook steaks for 2-3 minutes on each side until they reach desired doneness (135°F for medium-rare or 145°F for well-done).

Serve - remove steaks from grill, let rest for a minute, drizzle with reserved marinade, and garnish with green onions.