Make the Buttermilk Mixture: In a large bowl, whisk together the buttermilk, flour, cornstarch, egg, hot sauce, salt, and pepper until smooth.
Dredge the Chicken: Dip the chicken chunks one at a time into the buttermilk mixture, then coat in Panko breadcrumbs, pressing to ensure they stick.
Heat the Oil: In a large stockpot or Dutch oven, heat the vegetable oil over medium-high heat until it reaches 360°F on a deep-fry thermometer.
Fry the Chicken: Working in batches, fry the chicken in the hot oil until golden and crispy, about 2-3 minutes. Transfer the cooked chicken to a paper towel-lined plate to drain.
Make the Sweet Chili Sauce: In a small bowl, whisk together the mayonnaise, sweet chili sauce, honey, and Frank’s Hot Sauce until smooth.
Serve: Drizzle the fried chicken with the sweet chili sauce and garnish with chopped parsley, if desired. Serve immediately.