Add the sesame oil, soy sauce, red pepper flakes and egg to a large mixing bowl. Mix well, then fold in the tuna, red bell pepper and scallions. Mix well to coat everything evenly. Sprinkle with salt and fold in the panko breadcrumbs to lightly bind everything. Carefully form the mixture into 4 even-size patties and set on a platter. Refrigerate so the patties firm up and hold their shape when cooked, 15 to 20 minutes.
Heat a large nonstick skillet over high heat. Coat the pan with a little vegetable oil and cook the tuna patties 3 minutes per side (when done, the patties will be browned on the outside and medium-rare in the center).
Grill the hamburger buns over high heat until well charred and crispy.
Serve the tuna burgers slathered with the Spicy Sriracha Mayo, lettuce leaves and tomato slices on the toasted, seeded hamburger buns, paired with the dry Riesling.
Spicy Sriracha Mayo:
Combine the mayonnaise, sour cream, Sriracha, sesame oil, lemon juice, honey and scallions in a large mixing bowl. Stir well to combine, season with salt and pepper and place in the refrigerator until ready to serve.
When grilling the bread, you can grill 3 to 4 scallions at the same time for use in the Spicy Sriracha Mayo.