Pulse chiles in a spice grinder until coarsely ground.
Transfer ground chiles to a small bowl and add salt. Scatter lemon zest on a 6x6" piece of parchment paper and microwave on high for 1 minute.
Add thyme to parchment and microwave until dry, about 1 minute 30 seconds (time will vary).
Let cool and lightly crush zest and thyme; combine with ground chiles and salt. DO AHEAD: Spice mix may be made 1 week ahead. Store airtight at room temperature.
