Step 1

Finely grate zest of 1 lemon into a blender. Cut both lemons in half and tease out seeds. Squeeze juice into blender; you should have around ½ cup. Add chiles, garlic, parsley, oil, and ⅓ cup cold water and blend on high speed until smooth and very green.

Step 2

Pour mixture into a medium bowl, add tahini, and whisk until fully incorporated; season sauce generously with salt.

Step 3

Do Ahead: Sauce can be made 3 days ahead. Cover and chill.