Crush the peppercorns in a mortar and pestle or pulse a few times in a food processor—you’re looking for a mix of finely ground and crushed peppercorns.
Add peppercorns to a medium skillet along with the seeds and toast over medium heat, stirring occasionally, until fragrant, 2 to 3 minutes. (The quinoa will pop when it’s toasted.)
Transfer to a small bowl and let cool, then stir in the flaky salt. Store the mixture in an airtight container at room temperature for up to a month.