Combine sesame oil, 1 tablespoon of the soy sauce and Dijon mustard. Rub mixture over both sides of fish fillets. Cover with sesame seeds and lightly press seeds into both sides. Heat oil in a large skillet over medium heat. Add fish and cook until sesame seeds are lightly browned on one side. Carefully flip over and cook other side for 1 minute. Add remaining soy sauce, lemon and lime juice and gingerroot to pan and cook until fish is just a tad underdone. Remove from pan and transfer to plates. Top with chopped green onions.