If needed, cut chicken tenderloins into finger-sized strips.
Place the chicken strips in a bowl with the buttermilk, toss to coat, then refrigerate and marinate for at least 1 hour.
In a shallow dish, whisk together the flour, salt, black pepper, garlic powder, and paprika.
Beat the eggs in a separate shallow dish.
Place the panko breadcrumbs in a third shallow dish.
Dredge each marinated chicken strip in the seasoned flour, shake off excess, dip into the beaten eggs, then press into the panko to coat evenly.
Heat vegetable oil in a deep fryer or large skillet to about 350°F (175°C) to 1/2-inch to 1-inch depth.
Fry the coated chicken strips in batches until golden brown and cooked through, about 3–4 minutes per side depending on thickness.
Transfer cooked chicken fingers to paper towels to drain briefly, then serve hot.