Mix zucchini, Cheddar cheese, and onion together in a bowl. Stir eggs and biscuit mix into zucchini mixture until well combined.
Heat vegetable oil on the griddle or large skillet over medium heat. Scoop about 1/4 cup batter onto heated griddle; cook until pancakes are browned, 3 to 4 minutes per side. Repeat with remaining batter.