Preheat your oven to 375 degrees Fahrenheit and line a loaf pan with parchment paper and lightly grease it using vegan butter or coconut oil. In a bowl, add the milk and lemon juice, stirring it together and letting the mixture sit for 5-10 minutes or until it slightly thickens and everything "activates". In a large bowl, add the flour, baking powder, sugar, lemon zest, cinnamon, and sea salt and whisk until combined. Stir in the milk-lemon mixture, grated zucchini, and melted butter, mixing until combined and the batter become thick and smooth. Pour batter in the prepared loaf pan (evenly spreading it out).