Preheat the oven to 400°F and liberally coat 2 shallow baking sheets with nonstick spray.
Trim the ends from the zucchini, cut them in half crosswise, then cut each piece into lengthwise wedges about 1/2-inch thick.
Combine the flour, salt, garlic powder and black pepper in a large zip-top plastic bag. Add about 1/3 of the zucchini strips and shake the bag to coat them with the flour. Transfer to a plate and repeat with the remaining zucchini.
Whisk the eggs and milk together in a shallow dish. Thoroughly combine the panko crumbs and grated cheese on a large sheet of wax paper and set it next to the egg mixture.
Using tongs, dip the zucchini strips, one at a time into the egg mixture, being sure to coat them on all sides.
Next, coat them with the panko-cheese mixture. An easy way to do this is to place a strip of zucchini in the center of the pile of crumbs, then lift the edge of the wax paper to "bury" the zucchini in more crumbs. You'll lose very little of the egg mixture this way and the coating will adhere better.
Transfer the crumb-coated zucchini to the prepared baking sheets and spray the tops lightly with nonstick spray.
Bake until the coating is crisp and golden brown and the zucchini is tender but not mushy, 18 to 22 minutes. Be sure to rotate the baking sheets in the oven once or twice to ensure even browning.
Sprinkle the zucchini with a little salt and pepper as soon as it comes out of the oven. Serve immediately with warm marinara sauce for dipping if desired.