Preheat the oven to 170ºC. Grease a muffin tin with butter or non-stick cooking spray and dust lightly with flour.
Mix wet ingredients: In a medium bowl, combine the olive oil, light brown sugar, lemon zest, vanilla extract, and egg. Stir until well mixed.
Prepare the courgette (zucchini): Grate the courgette using the medium side of a cheese grater. Squeeze out the excess water from the grated courgette over the sink, then add it to the wet ingredients. Stir until fully incorporated.
Combine dry ingredients: Add the flour, salt, baking powder, and bicarbonate of soda to the wet mixture. Stir gently until just combined, being careful not to overmix.
Portion the batter: Divide the batter evenly among the muffin cups. Each cup should hold between 75-85g of batter.
Bake: Place the muffin tin in the preheated oven and bake for 15 minutes. Check the muffins by inserting a toothpick into the center; if it comes out clean, they’re done. If not, continue baking, checking every 5 minutes, until the muffins are fully baked (this may take up to 25 minutes).
Cool: Once baked, remove the muffins from the oven and allow them to cool in the tin for 5 minutes before transferring them to a wire rack to cool completely.