Step 1

Heat a 12-inch skillet (preferably cast-iron) over medium-high until water flicked onto the surface sizzles and evaporates within seconds, about 3 minutes. Place the avocado halves cut side down in the pan, then add the onion slices, poblano chili and tomatillos. Cook, occasionally turning everything but the avocado halves, until mostly charred all over, 7 to 10 minutes; transfer each item when done to a large plate. Cool completely.

Step 2

Remove the stem and seeds from the poblano (there is no need to remove the skin). Finely chop the poblano, onion and tomatillos, then place in a medium bowl.

Step 3

Using a spoon, scoop the avocado flesh into the bowl. Add the cilantro, lime juice and ½ teaspoon salt. Mash to a coarse puree, then taste and season with salt, pepper and, if desired, additional lime juice. Transfer to a serving bowl and sprinkle with chili powder.