Make the Bang Bang Sauce. Whisk together mayonnaise, Thai sweet chili sauce, Sriracha, and honey in a medium-sized bowl until well combined.
Adjust Sriracha to taste, adding more for extra heat if desired.
Set the sauce aside in the refrigerator to let the flavors meld while preparing the chicken.
Prepare the Chicken Tenderloins. In a large mixing bowl, combine buttermilk, all-purpose flour, cornstarch, egg, Sriracha, garlic powder, kosher salt, black pepper, and cayenne pepper (if using). Whisk until you have a smooth, thick batter.
Add the chicken tenderloin to the batter and mix, ensuring it's well coated.
In a separate shallow dish, spread out the panko breadcrumbs.
Carefully transfer each battered chicken tenderloin to the panko breadcrumbs, pressing the breadcrumbs onto the chicken to coat it thoroughly. Place the coated chicken on a baking sheet. In a large frying pan, heat enough oil over medium-high heat for frying. Once the oil is hot, carefully add the breaded chicken tenders in batches, ensuring the pan is not overcrowded.
Fry on each side until golden brown and crispy, approximately 4-5 minutes per side. Adjust the heat to maintain a consistent temperature.
Place the cooked chicken on a paper towel-lined plate to absorb excess oil.
Drizzle or brush the Bang Bang Sauce over the crispy chicken, ensuring each piece is generously coated.
Garnish with chopped parsley before serving.