In a bowl, mix soy sauce, vegetable oil and ground ginger.
Mix the marinade until smooth. You can add dried herbs if desired.
Place the tuna fillets in the marinade and leave for 20 minutes.
Heat a frying pan, grease it with vegetable oil and place the tuna on it.
Fry the tuna for 3 minutes on each side. This will give you medium-rareness. If you want to cook the tuna thoroughly, fry it for another 6 minutes.
Cut the finished fillet into slices. Place the fish on spinach leaves, garnish with cherry tomatoes and pour over teriyaki sauce. Enjoy.