Preheat the oven to 170ºC (335ºF) and grease and line a 20 x 10 cm (8 x 4 in) loaf tin with non-stick baking paper. Be sure to leave a couple inches of overhang for easy removal.
In a large bowl, whisk together the flour, coconut sugar, poppy seeds, baking powder, baking soda, and salt. Set aside.
In a medium bowl, whisk together the melted butter, eggs, lemon zest, milk, lemon juice, and vanilla extract until well combined. Stir in the grated courgette, making sure the strands are loose and not clumped together.
Make a well in the dry ingredients and add the wet ingredients. Stir everything together until combined and smooth.
Pour the batter into the prepared loaf tin and bake for 40-45 minutes, or until a toothpick inserted comes out clean or with a few crumbs attached.
Remove the courgette loaf from the oven and allow to cool in the tin for 15 minutes. Then lift the cake from the tin, remove the baking paper, and allow it to finish cooling on a wire rack.