How to Make It
Prepare the Soup: Heat oil in a large pot over medium. Add sweet potato, onion, coriander, cumin, salt, pepper, and garlic; cook, stirring occasionally, until onion is golden, 5 to 7 minutes. Add broth and bring to a boil. Reduce heat to medium and simmer, covered, until sweet potato is tender when pierced with a fork, 16 to 18 minutes. Working in batches, transfer mixture into a blender. Remove center piece of blender lid (to allow steam to escape), secure lid on blender, and place a clean towel over opening in lid to prevent splatters. Process until smooth, about 30 seconds, slowly adding water to thin to desired consistency.
Prepare the Dukkah: Stir together pistachios, sesame seeds, oregano, thyme, zest, and salt in a small bowl.
Serve soup topped with dukkah and a drizzle of olive oil.