In a large bowl, combine the buttermilk, garlic powder, onion powder, paprika, salt, and black pepper. Mix well to create the marinade.

Add the chicken tenderloins to the marinade, ensuring they are fully submerged. Cover the bowl and refrigerate for at least 1 hour, or up to overnight for maximum flavor.

In a separate shallow dish, whisk together the flour, baking powder, and cayenne pepper (if using). This mixture will provide the crispy coating for your tenders.

Heat about 1 inch of vegetable oil in a large skillet over medium-high heat. The oil is ready when it reaches 350°F (175°C). You can test this by dropping a small amount of the flour mixture into the oil; it should sizzle immediately.

While the oil heats, remove the chicken from the marinade and allow any excess liquid to drip off. Dredge each tenderloin in the flour mixture, pressing lightly to ensure the coating adheres well.

Carefully place the coated chicken tenders into the hot oil, being sure not to overcrowd the skillet. Fry in batches if necessary, cooking each side for about 4-5 minutes, or until golden brown and cooked through.

Use a slotted spoon to transfer the fried chicken tenders to a paper towel-lined plate to drain excess oil. Let them rest for a few minutes before serving.