First of all, obviously, you need a big and thick slice of tuna fish fillet.
It must be very fresh, so trust your fishmonger.
Then you need fresh tomatoes
Olive oil
Fresh leaves of basil
A glass of dry white wine
Various spices at your pleasure…
I suggest you use dried parsley
Cayenne pepper
Mild curry
Chervil
And minced dried tomatoes
Ah...and salt, of course!