Cut the zucchini in half lengthwise and hollow out their flesh with a spoon well.
Chop the zucchini flesh and set it aside.
Sprinkle zucchini shells inside with salt, turn upside down, and let drain while you are preparing the stuffing. When ready to use the shells, wipe off excess liquid and salt with paper towels.
Mix chopped green olives with pressed garlic, olive oil, chopped walnuts, basil, egg, reserved zucchini flesh, and bread crumbs. Add drained tuna, salt, pepper, and hot chili flakes and mix well with a spoon or a fork.
Fill the zucchini shells with the stuffing mix reasonably tightly.
Transfer stuffed zucchini to the air fryer.
Cook at 350F for 30 minutes. No flipping or turning is needed. Cooking time may be affected by zucchini size and how your air fryer cooks, so start checking at about 20 minutes the first time you cook them. Zucchini boats are done when the tops are well-browned.
Serve hot or cold, as a snack, appetizer, or with a salad as a main dish. Drizzle with some olive oil and garnish with chopped chives and basil leaves before serving. You can also serve them with marinara or dipping sauce, ranch dressing, or tartar sauce.