If using fresh lemons, zest 4–5 medium lemons to yield about 1/4 cup of peel.
Spread zest on a parchment-lined baking sheet and either air-dry for 1–2 days until brittle or bake at 150°F for 30–60 minutes, checking until completely dry and crumbly.
Add the dried lemon peel, black peppercorns, garlic powder, onion powder, and fine sea salt to a spice grinder or small food processor.
Pulse until the mixture reaches your desired consistency, stopping before it turns pastey.
Transfer the seasoning blend to an airtight jar and store in a cool, dark pantry for up to 6 months.