Preheat oven to 400 degrees F. Well grease a 10-inch cast-iron skillet, and place it into the oven while it preheats. (can use a 9x9 Pyrex pan but cast iron works better).
Place the zucchini, milk, onion, eggs, and melted butter into a blender, and blend until thoroughly mixed and the zucchini and onion have been chopped into very small pieces.
Mix together the cornmeal, flour, dill, baking powder, salt, pepper and cheddar cheese in a large bowl. Pour the zucchini mixture into the cornmeal mixture, stirring to combine.
Carefully pour the batter into the hot greased skillet, smooth it out with a spoon, and bake until the cornbread is golden brown and a toothpick inserted into the center comes out clean, about 30 - 40 minutes.