Preheat the oven to 150F. Line a baking sheet with parchment paper and set aside.
Rinse the lemons to remove any surface dirt and pat dry with a kitchen towel. Using a vegetable peeler, remove the zest from each lemon, being careful to remove just the yellow zest and not the bitter white pith. Place the lemon zest onto the parchment lined baking sheet, then transfer to the oven to dry, about 3 hours. (Or use a dehydrator, if you have one). When the zest is completely dry, remove it from the oven and allow it to cool to room temperature.
Using a small food processor or spice grinder, pulse the dehydrated lemon zest, black pepper, garlic powder and salt until the mixture is ground, with a few larger pieces of black peppercorn remaining. Store in an airtight container for up to 6 months, or in the freezer for up to 1 year.