Sesame Tuna Burgers with Fried Shoestring Zucchini

Put oven rack in middle position and preheat oven to 350°F. Toast sesame seeds in a shallow baking pan in oven, stirring occasionally, until golden, 12 to 15 minutes. Cool completely. Transfer 2 tablespoons seeds to a small bowl and 1/4 cup to grinder. Transfer remaining 3/4 cup to a wide shallow bowl.
Halve 3 zucchini crosswise, then cut lengthwise into 3/4-inch shoestrings using slicer. Toss with 1 teaspoon salt in a large sieve set over a bowl and drain 30 minutes.
Squeeze handfuls of zucchini to remove moisture, then roll up in a triple layer of paper towels and squeeze to remove remaining moisture.
Finely chop tuna with a large wet knife (about 3/4-inch pieces). Stir together soy sauce, 2 tablespoons oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a bowl, then stir in tuna. Divide tuna mixture into 4 portions. Pack 1 portion in a 1/2-cup measure, then invert onto seeds in shallow bowl. Gently press tuna to form a patty 3 1/2 inches in diameter, then coat completely with seeds and transfer to a wax-paper-lined plate. Form, coat, and transfer 3 more burgers in same manner. Chill, covered with plastic wrap, until ready to cook. Discard any sesame seeds remaining in shallow bowl.
Grind seeds that are already in grinder, pulsing until ground to a flour, then add to remaining seeds (2 tablespoons) in small bowl.
Remove julienne attachment from slicer, then cut remaining zucchini lengthwise into 3/4-inch-thick ribbons using slicer. Gently toss with 1/4 teaspoon salt in a large bowl and set aside (zucchini will wilt and become tender).
Heat 1 inch oil in a 5- to 6-quart heavy pot over moderate heat until thermometer registers 330°F.
Toss all of shoestring zucchini with half of sesame mixture in another large bowl, then fry in 4 batches, turning occasionally with a slotted spoon, until zucchini are golden, about 2 minutes per batch. (Return oil to 330°F between batches.) Transfer zucchini as fried to paper towels to drain. Toss each batch of zucchini immediately with some of remaining sesame mixture.
Heat 3 tablespoons oil in a 12-inch heavy skillet over moderately high heat until hot but not smoking. Cook burgers, turning over once, about 2 minutes total for medium-rare tuna (seeds should be golden brown).
Drain zucchini ribbons and divide among 4 plates, then top with burgers and fried shoestring zucchini. Serve burgers with additional soy sauce on the side.