For the Tuna & Ginger Burgers: Combine the wasabi, mustard and water in a small bowl. Scrape it into a food processor along with the pepper, salt, ginger, garlic and peanut oil. Pulse it all together to make a flavorful paste. Add the tuna and pulse just to combine- be carful not to over process the tuna as you want your burgers to have texture. Form the mixture into four burgers and set in the refrigerator for at least an hour (up to overnight) to let the flavors really settle in.
Meanwhile, heat the olive oil over medium-high heat in a skillet. Add the shallots and saute for about 10 minutes, until they get soft and sweet and a little brown. Reserve.
Preheat your grill or grill pan over high heat.
Rub the tuna burgers with a little peanut oil and grill for 2 to 3 minutes a side, to desired doneness. Grill the buns alongside the burgers. Spread the buns with the mayo, pile on the sauteed shallots and a bit of arugula, and tuck in the burgers.
For the Soy & Sesame Mayo: Whisk everything together. (Makes 1/2 cup)