Place the tuna in a food processor and pulse until it reaches the consistency of ground beef. In a large bowl, combine the ground tuna with the garlic, ginger, soy sauce, scallions, bell pepper, sesame oil and grill seasoning. Form the meat into 4 large patties.
Heat 1 tablespoon of vegetable oil in a large nonstick skillet over high heat and 1 tablespoon of vegetable oil in a medium nonstick skillet over medium-high heat.
Add the tuna patties to the large skillet and cook for 2 minutes on each side for rare, or for 4 minutes on each side for well done. While the burgers work, saute the mushrooms for 5 minutes in the medium skillet. When the mushrooms are tender, salt them to taste.
To assemble the burgers, spread the roll bottoms with the wasabi mustard; top with the lettuce, burgers and mushrooms. Slather the bun tops with the mango chutney and set in place. Pass around extra mustard and chutney at the table, if desired. Serve the tuna burgers with pickled ginger and root vegetable chips.