Add butter, onion and garlic to a skillet and cook until onion is tender, about 3-5 minutes. Add corn to pan and cook for 1-2 minutes more. Stir in zucchini.
Add flour, cornmeal, salt, pepper and baking soda to a bowl and mix well. Stir in buttermilk and mix. Combine with zucchini mixture and mix well.
Heat a skillet with 1" of vegetable oil until hot. Use a 3 tablespoon portion scoop to scoop zucchini mix into skillet. Gently press to flatten to about 1/2". Fry on both sides, about 5 minutes each, until golden brown. Drain on paper towels.