Preheat your oven to 350 degrees, line a muffin pan with liners and set aside.
In a small bowl, mix together the flour, baking powder, baking soda and salt, set aside.
In a large bowl, whisk together the eggs and sugar for 1 to 2 minutes, until thick and pale. To the same bowl add the oil, zucchini, vanilla, thyme, lemon juice, and lemon zest. Whisk until combined and then finally, fold in the dry ingredients.
Divide the batter evenly in your prepared muffin tins. They will be quite full. Set aside.
In a small bowl, mix together the ingredients for the topping, and using your fingers break the butter evenly among the dry mixture, then add a sprinkle onto each muffin.
Put the muffins into the oven to bake for about 20 minutes or until golden brown and fully cooked through. Place on a wire rack to cool completely.