Combine the soy sauce, sesame oil, honey, rice vinegar, ginger, and garlic in a shallow dish. Place the tuna steaks in the marinade, turning to coat. Marinate for at least 15 minutes, allowing the flavors to infuse.

Mix the sesame seeds (white and black if using) on a separate plate. Season the tuna steaks with salt and pepper, then press each side into the sesame seed mixture, ensuring a crust forms.

Heat vegetable oil in a skillet or pan over medium-high heat. Sear the tuna steaks for 1-2 minutes per side for a rare to medium-rare doneness or longer if desired.

Remove the tuna steaks from the pan and let them rest for a few minutes. Slice the tuna into 1/2-inch thick slices.

Garnish with sliced green onions and additional sesame seeds.