Step 1: Prepare the Chicken

1. In a large bowl, whisk together the buttermilk, garlic powder, smoked paprika, salt, and black pepper.
2. Add the chicken breasts to the mixture, ensuring they are fully coated. Cover and marinate in the refrigerator for at least 30 minutes, or up to 4 hours for maximum flavor.

Step 2: Prepare the Coating

1. In a shallow dish, combine the flour and cornstarch. Mix well.
2. Remove the chicken from the buttermilk marinade, allowing excess liquid to drip off, and coat each piece in the flour mixture. Press the coating firmly onto the chicken to ensure it adheres well.

Step 3: Fry the Chicken

1. Heat about 2 inches of vegetable oil in a large skillet or Dutch oven over medium heat until the oil reaches 350°F (175°C).
2. Fry the chicken breasts in batches for 3–4 minutes per side, or until golden brown and cooked through (internal temperature should reach 165°F).
3. Transfer the cooked chicken to a wire rack or paper towel-lined plate to drain excess oil.

Step 4: Make the Bang Bang Sauce

1. In a small bowl, whisk together the mayonnaise, sweet chili sauce, sriracha, honey, and lime juice until smooth and creamy. Taste and adjust the spice level if needed.

Step 5: Assemble the Sandwiches

1. Lightly toast the brioche buns for added texture and flavor.
2. Spread a generous layer of Bang Bang sauce on both the top and bottom halves of each bun.
3. Place a piece of fried chicken on the bottom bun.
4. Top with shredded lettuce, cucumber slices, red onion, and cheese (if using).
5. Add additional sauce or a drizzle of sriracha or sweet chili sauce for extra flavor. Cover with the top bun.

Step 6: Serve

1. Serve the sandwiches warm with your favorite sides, such as fries, coleslaw, or a side salad. Enjoy immediately for the best flavor and texture.