Preheat oven to 400°F. Place an oven-safe wire rack on a large baking sheet; set aside.
Pat 1½ pounds boneless skinless chicken breasts dry and cut into roughly 1-inch cubes; set aside.
Set up three shallow stations: (a) in a shallow bowl beat 2 large eggs until combined, (b) spread 1/3 cup all-purpose flour on a plate, (c) in a medium bowl combine 1½ cups panko, 1/2 teaspoon kosher salt, 1/4 teaspoon garlic powder, and 1/4 teaspoon onion powder; whisk to combine.
Working with one piece at a time, lightly coat each chicken cube in the flour, shaking off excess; dip into the beaten eggs and allow excess to drip off; then press and roll the piece in the panko mixture until fully coated. Place coated pieces in a single layer on the prepared wire rack (do not overcrowd).
Bake on the middle oven rack for 20 minutes, or until the chicken is golden and cooked through (internal temperature 165°F if using an instant-read thermometer).
While the chicken bakes, make the sauce: in a small saucepan over medium-low heat combine 4 tablespoons low-sodium soy sauce, 2 tablespoons sesame oil, 3 tablespoons packed light brown sugar, 1/4 cup rice vinegar, 1 tablespoon grated fresh ginger, and 3 cloves minced garlic. Bring the mixture to a light simmer.
In a small bowl whisk 1½ tablespoons cornstarch with the 2½ tablespoons water from the ingredient list until smooth. Stir this slurry into the simmering sauce and cook, stirring, until the sauce just thickens, about 30–60 seconds. Stir in 1/4 cup sesame seeds.
When the chicken is done, transfer the pieces to a large mixing bowl. Pour the hot sauce over the chicken and toss gently to coat evenly.
Sprinkle 1/4 cup chopped scallions over the coated chicken and serve immediately.