If you’d like to keep the zucchini warm between batches, preheat the oven to 200°F. Trim off the ends of the zucchini and cut into quarters length-wise. Place each quarter against the cutting board, flat side down, then cut crosswise into 3/4-inch thick half-moons so that you have chunks that are about 3/4 inch in size each. Place in a large mixing bowl.
Drizzle the zucchini with the oil. Toss to coat.
In a separate bowl, stir together the panko, Parmesan, flour, salt, onion powder, and pepper. Sprinkle over the zucchini, then toss to coat the zucchini as evenly as possible.
Preheat the air fryer to 400°F. Place half of the zucchini in the air fryer basket in an even layer (no need to coat it with nonstick cooking spray).
Air fry zucchini for 7 to 9 minutes, shaking a few times throughout, until the breadcrumbs are golden and the zucchini is tender but not mushy. Transfer to a serving plate or a parchment-lined baking sheet if keeping warm in the oven. Repeat with remaining zucchini.
TO STORE: Refrigerate zucchini in an airtight storage container for up to 4 days.
TO REHEAT: Rewarm leftovers on a baking sheet in the oven at 350°F or in the air fryer.
TO FREEZE: I do not recommend freezing zucchini, as it becomes soggy once thawed. If you insist, you can freeze zucchini in an airtight freezer-safe storage container for up to 3 months. Let thaw overnight in the refrigerator before reheating.