Add sesame seeds to a small/medium frying pan and spread into a thin layer. Turn the heat to medium and gently toast the seeds until lightly toasted and fragrant, around 4-5 minutes. Make sure to watch the seeds. Once they begin to toast, they can burn pretty quickly.
Remove the seeds from the pan to stop toasting and transfer them to a smallish bowl. Add the other ingredients and stir well to combine. Taste and adjust salt as preferred. I use a full teaspoon of salt, but that's me. Try it with a half-teaspoon and add more if you prefer.
Store in an airtight container in a cool place out of direct sunlight for up to 3 months. Always check for moisture inside the jar. If the jar has moisture, discard the mix.
Notes
To get the most flavour from your za'atar , toast the cumin seeds until fragrant, then grind.