Stir ½ cup mayonnaise, ¼ cup sweet chili sauce, and 4 teaspoons of the Sriracha together in a large bowl. Transfer half of the sauce to a small bowl for serving.

Whisk the remaining 1 teaspoon Sriracha, 2 large eggs, and 2 tablespoons all-purpose flour together in a medium shallow bowl or pie plate. Stir 2 ½ cups panko breadcrumbs, 1 teaspoon of the kosher salt, and 1 teaspoon garlic powder together in a second shallow bowl or pie plate.

Season 1 ¾ pounds boneless, skinless chicken breast pieces with the remaining ¾ teaspoon kosher salt. Working with a few pieces at a time, add the chicken to the egg mixture, turn to coat, then transfer to the panko mixture. Gently press and flip the chicken into the panko mixture until completely coated. Place on a rimmed baking sheet in a single layer.

Heat 1 cup neutral oil in a large high-sided skillet over medium heat until 350°F. Line a second baking sheet with a wire rack and/or paper towels. Fry about 8 pieces of chicken at a time: Add to the hot oil and fry, flipping halfway through, until cooked through and golden-brown all over, 3 to 5 minutes total. Transfer to the rack or paper towels.

Transfer the chicken to the large bowl of sauce and toss until coated. Garnish with thinly sliced scallions if using. Serve with the remaining sauce drizzled on the top or on the side for dipping.