Set the oven to broil on high, then place the poblanos directly on the rack. Cook for 8 to 12 minutes until the skin is blistered.
Every oven is different so check halfway through and turn/flip the peppers as needed to ensure even blistering.
Once the poblanos are charred, place them in a bowl or container with a lid. Let cool 10 minutes.
You should now be able to easily peel the skin off the peppers. Next, remove the stem and any seeds inside.
I slice along the length of the pepper to open it up and scrape the seeds out.
Blend Sauce
Finally, combine the peeled and seeded poblanos, cilantro, Greek yogurt, salt, lime juice, zest, and garlic in a food processor and blend until smooth. Taste and adjust as needed.
Alternatively, a handheld immersion blender works well too.
Notes
For a thinner sauce, use more lime juice and less Greek yogurt. To thicken the sauce, adjust with more Greek yogurt.