Whisk buttermilk, whole wheat flour, all-purpose flour, Parmesan cheese, egg, olive oil, salt, baking powder, and pepper together in a medium bowl until smooth. Stir in corn, zucchini, onion, basil, and garlic.
Coat a large nonstick skillet with cooking spray and heat over medium heat. Pour 1/4 cup batter into the pan to make a 3-inch fritter. Repeat to make 3 more fritters in the skillet. Cook until edges are firm and bottom is golden brown, about 2 minutes. Flip and cook until the other side is golden brown, about 2 minutes more. Transfer to a baking sheet and place in the preheated oven to keep warm. Repeat to make remaining pancakes.