Heat a large skillet over medium-high heat. Rub the tuna with the ginger, and then roll in sesame seeds. Sprinkle the soy sauce over the top. Add sesame oil to pan and bring up to temperature. Add tuna, searing for 1-2 minutes a side (4 sides). Do not allow sesame seeds to burn. Remove to a cutting board, allow to rest for 2 minutes, then slice and serve.