If you can't find toasted sesame seeds: In a small skillet, dry toast the sesame seeds until fragrant and lightly golden in color. Remove from heat and cool.
Crush the sumac and salt with the mortar and pestle (or in a small bowl and the end of a wooden spoon). Add the thyme, oregano and optional dried cilantro and grind together. Stir in the sesame seeds and mix thoroughly. Taste, and adjust to taste with a bit more salt, or sumac.
Store in an airtight container. This makes about 1 cup.