Actually, the fish market I went to had fillets of tuna already wrapped in cellophane for easy purchase. The fillets were large--nine to ten ounces apiece--and they were also exactly what one looks for in a piece of tuna. They were pinkish red with no discoloration and the sign said they had been caught that day.
These things are important when it comes to tuna in particular, because most people don't cook tuna all the way through. If you're going to buy it for your own use, then, you have to make sure the product is really top rate.
I stopped by my favorite vegetable stand for some scallions and green beans. Back home, I combined a few tablespoons of sesame oil, soy sauce, wasabi, pickled ginger, ground ginger, sesame seeds, fresh lime juice, some baby bok choy, and one sliced scallion in a tupperware container. If you're wondering why I keep wasabi and pickled ginger in my house, well, I don't. I saved the leftover wasabi balls and condiments from the previous night's sushi, figuring I'd use it eventually.
I cut my tuna steak in half (the recommended portion size for a piece of tuna is four to six ounces) and coated it with the marinade with my hands. I then put the fish in the tupperware, closed it, and left it in the refrigerator for the rest of the day.
Which meant that, hours later, when I returned from a rigorous workout at the gym, the fish was ready to go. I heated a frying pan and wilted the bok choy for a few minutes before getting the fish on the heat. On a very high flame, I seared both steaks, one minute on each side. I ate the steak over brown rice with green beans that I had steamed. For extra flavor, I added tamari to my rice.
For me, tuna is the perfect substitute for a grilled steak. It is substantial in a way that some fragile white fish are not and it offers a comparable mouthfeel to meat. Seared rare, it's almost as good as a rib eye. Almost.
The fish was very fresh and the bright, spicy marinade proved the perfect counterpoint for dense the meat. Perhaps the best part is that last night's leftovers will be today's lunch, not bad for seven bucks at the local fish market.