Combine zucchini and onion in a large bowl.

Mix flour, cornmeal, salt, pepper, and garlic powder together in a small bowl until well combined.

Pour flour mixture over zucchini mixture; cover the bowl and shake until vegetables are evenly coated. Let the coated vegetables sit until the flour mixture becomes slightly moist and clings to the vegetables, about 30 minutes.

Heat oil in a large skillet over medium-high heat. Fry vegetables in batches in the hot oil until golden brown and crisp, turning as needed to cook evenly. Drain briefly on paper towels before serving.