Step 1: Build a charcoal fire and rake out the embers. Fan the fire to dislodge any loose ash. Lay the onion, poblanos, jalapenos, tomatoes, and tomatillos directly on the embers. Grill until charred on all sides, but still raw in the center. The onion and poblanos will take 8 to 10 minutes, the jalapenos, tomatoes, and tomatillos about 6 minutes. Lay the garlic in its foil on the embers and roast until soft, about 4 minutes. Transfer the veggies to a heatproof platter and let cool.
Step 2: Scrape any really burnt skin off the vegetables (a few black specks add character). Coarsely chop the vegetables in a food processor. Work in the cilantro, lime juice, oil, and salt and pepper to taste. Transfer to a serving bowl.