1 pound English cucumbers, halved, seeds removed
1 pound tomatillos, husks removed, rinsed
1/2 medium onion, thinly sliced, rinsed under cold water
1/2 poblano chile, seeds removed
1 garlic clove
1/4 cup olive oil
1/4 cup unseasoned rice vinegar
1 tablespoon chopped parsely
1 tablespoon chopped cilantro, plus leaves for serving
Kosher salt, freshly ground pepper
Blend cucumbers, tomatillos, onion, chile, garlic, oil, vinegar, parsley, and chopped cilantro in a blender until very smooth; season with salt and pepper. Transfer to an airtight container, cover, and chill at least 2 hours.
Serve topped with cilantro leaves.