Cut the zucchini into spears and soak in the buttermilk for at least 10 minutes.
Whisk the flour, garlic powder, paprika, salt, and pepper in a shallow dish. Whisk the eggs in a second dish. Pour the panko into a third dish.
Pat the zucchini spears dry. Dredge each spear in flour, then egg, then panko. Dip a second time in egg and panko for a double coating.
Heat 2 inches of oil in a heavy-bottomed pot to 375°F.
Fry the zucchini in batches of 5–6 for about 3 minutes, until deep golden.
Drain on a wire rack and salt immediately.
Whisk together the mayonnaise, sour cream, ranch seasoning, and buttermilk for the dip. Serve the zucchini hot alongside the dip.