Combine the sesame seeds in a shallow bowl. Lightly rub the tuna in the olive oil, then sprinkle liberally with salt and pepper. Press the tuna into the sesame seeds, applying firm pressure so the seeds stick. Cover completely and chill in the refrigerator, uncovered, for 5 minutes, to allow the seeds to stick.
For the vinaigrette: In a medium bowl, whisk together the grated ginger, ponzu, soy, vinegar, sesame oil and Fresno. Pour into a serving bowl and set aside.
In a large nonstick pan, heat 1/2 inch canola oil to 320 degrees F.
Add the shallots to the oil in small batches and fry until golden brown, about 2 minutes. Remove to a paper towel-lined plate and drain. Season with salt.
Add 1/4 cup olive oil to another large, nonstick pan and turn the heat on high until hot. Add the sesame-crusted tuna and sear all over for 30 seconds on each side. Remove from the pan and slice 1/2-inch thick.
Shingle the tuna on a platter, then sprinkle over the fried shallots and sliced scallions. Serve with the vinaigrette alongside.