The tuna burger was born in restaurant kitchens as a way of using up scraps left over from fancy cuts, but we think it's worth buying tuna just to make these.
Cut tuna into 1/4-inch chunks with a very sharp knife, trimming away any dark, bloody parts. Coarsely chop tuna by hand until it begins to hold together. Transfer to a bowl over a bowl of ice. Add garlic, olive oil, sesame oil, anchovy, basil, celery, ginger, salt, and pepper; combine well.
Heat grill to medium high. Form tuna into 6 patties, and place on hot grill, or chill for up to 6 hours until ready to cook. Grill from about 3 or 4 minutes per side for rare to 7 or 8 for well done. Alternatively, cook in a nonstick skillet or grill pan over medium-high heat for about 2 to 3 minutes per side for rare to 5 or 6 for well done.
Serve with mizuna on buns brushed with sesame oil and toasted, if desired. Serve with pickled ginger and wasabi mayonnaise.
Mizuna can be replaced with watercress.