Marinate the Chicken: In a large bowl, combine the chicken pieces with buttermilk. Cover and refrigerate for at least 2 hours, or up to overnight.
Prepare the Breading: In a shallow dish, mix together the flour, garlic powder, onion powder, paprika, salt, black pepper, and cayenne pepper (if using). In another dish, beat the eggs. Place the panko breadcrumbs in a third dish.
Bread the Chicken: Remove the chicken from the buttermilk, allowing any excess to drip off. Dredge each piece in the flour mixture, shaking off the excess. Dip into the beaten eggs, then coat with the panko breadcrumbs, pressing gently to adhere.
Fry the Chicken: Heat about 2 inches of vegetable oil in a large skillet over medium-high heat until it reaches 350°F (use a thermometer for accuracy). Fry the chicken tenders in batches for 3-4 minutes per side, or until golden brown and cooked through. Drain on paper towels.