In a bowl, whisk together soy sauce, sesame oil, ginger, garlic, and lime juice.

Place the Ahi tuna fillets in a shallow dish and pour the marinade over them. Let marinate for 10 minutes.

Heat a skillet over high heat. Remove the tuna from the marinade and sear for 1-2 minutes on each side, until the outside is browned but the inside is rare.

Slice the tuna against the grain and serve garnished with sesame seeds and scallions.