Preheat the oven to 325F. Line a muffin tin with silicone molds or grease it very well with butter.
Take two large bowls, to have at hand. Use the first one to combine the flour with salt, baking powder and pepper. In the second one, beat the egg. Add the oil and milk and mix well.
Pour the wet ingredients over the dry and whisk just until evenly combined.
Use a wooden spatula or spoon to gently fold in the zucchini, cheese, herbs and onion. You will obtain a thick batter which will not resemble at all with the regular muffin mixture which is more fluid. That is perfectly fine and you shouldn’t worry. The batter will rise and turn into delicious savory muffins.
Divide the mixture equally between 15 muffin cases, making sure you only fill them for about ¾ of their capacity.
Bake for about 30-35 minutes. They should have a beautiful golden color and a toothpick inserted in the middle of a muffin needs to come out clean.
Remove from the oven and set aside for 8-10 minutes to cool a bit before serving.
In case you have any muffins left, take them to an airtight container and keep at room temperature for maximum 3 days.