In a bowl, combine the buttermilk and hot sauce. Place the chicken breasts in the buttermilk mixture, ensuring they are completely submerged. Cover the bowl and refrigerate for at least 2 hours, to allow the chicken to marinate.

In a separate bowl, mix together the all-purpose flour, paprika, onion powder, garlic powder, cayenne pepper, salt, and black pepper.

Remove the marinated chicken breasts from the buttermilk mixture, allowing any excess liquid to drip off.

Dredge the chicken breasts in the seasoned flour mixture, making sure to coat them thoroughly. Shake off any excess flour.

In a large skillet or frying pan, heat vegetable oil over medium-high heat until it reaches 350°F.

Carefully place the coated chicken breasts in the hot oil and fry for about 6-8 minutes on each side, or until they are golden brown and fully cooked through. The internal temperature of the chicken should reach 165°F. Drain the fried chicken on a paper towel-lined plate to remove any excess oil.

To assemble the sandwiches, spread mayonnaise on the toasted hamburger buns. Place a fried chicken breast on the bottom half of each bun, and top with lettuce leaves and sliced tomato.

Serve the crispy buttermilk fried chicken sandwiches immediately.