To make the za’atar, in a dry skillet over medium heat, toast the sesame seeds until lightly browned, about 3 minutes. Transfer to a bowl to cool. Add the rest of the ingredients to the bowl and stir to combine. Store any extra in a small jar or airtight container in a cool dark place for up to 6 months.
In a small bowl, combine the onion and lemon juice and stir to coat, letting the mixture soak while you prep the other ingredients. (This mellows the onion, making it easier to digest.)
In a large bowl, add the radishes, cucumber, tomatoes, and
1 teaspoon of the za’atar, stirring until the vegetables are coated. Add the herbs and lettuce with another 1⁄2 teaspoon za’atar, turning with tongs or salad forks until well mixed.
Just before serving, add the onions with lemon juice and oil, tossing until the salad is well coated. Taste for seasoning and finish with a few pinches of coarse salt.
Kitchen notes: Za’atar is
an iconic Middle Eastern spice blend that varies by country. The za’atar instructions will yield about ¼ cup, but you need only 1½ teaspoons for the salad, so store the rest for another day.”