In a bowl, mix buttermilk, garlic powder, onion powder, paprika, salt, and black pepper, then add the chicken pieces and marinate for at least 20 minutes (or up to overnight for more flavor).
In a shallow dish, combine flour and panko breadcrumbs. Remove chicken from the marinade, let excess drip off, and coat each piece in the flour–breadcrumb mixture.
Heat oil in a skillet to about 175°C (350°F). Fry chicken in batches for 3–4 minutes per side, until golden, crispy, and cooked through, then drain on paper towels. (You can also air fry according to your appliance instructions.)
In a small bowl, whisk together mayonnaise, sweet chili sauce, Sriracha, honey, lime juice, and garlic powder until smooth and creamy. Adjust sweetness or heat to taste.
Lightly toast the slider buns. Spread a layer of Bang Bang sauce on the bottom bun of each slider.
Place a piece of crispy chicken on each bun, top with shredded lettuce, red onion, and any optional toppings, then drizzle with more Bang Bang sauce and finish with the top bun.
Garnish with sliced green onions and serve immediately while the chicken is hot and crispy.