Roast poblano peppers on the grill until peppers soften and skins blister. This should take about 15 minutesRemove and set aside. When cool enough to handle, remove charred skins and seeds. Cut into ½-inch strips.
In a medium size, heat 2 tablespoons vegetable oil. Brown pork for about 4 to 5 minutes. Remove and set aside.
Add remaining tablespoon of oil to pan. Saute garlic and onion until soft, about 2 minutes. Add poblano peppers, ground cumin, and ground chipotle pepper.
Return pork to the pan, followed by ¾ cup (180ml) water. Bring it up to a boil, reduce heat, and allow it to simmer for 30 minutes.
Add tomatillos and salt. Cover and continue to cook for another 15 minutes.