Pre-heat the broiler to high.
Char the peppers all over until skins are blackened. Spray the corn, if using, with cooking spray and broil until charred evenly.
Place the peppers in a bowl and cover until cool. Skin and seed the poblanos, then coarsely chop. Cut the corn from the cob.
Turn the oven temperature to 450°F.
Dress the tomatillos with a tablespoon of EVOO and arrange cut-side down on a baking sheet. Arrange the onion and garlic on a second sheet; toss with the remaining EVOO and season with cumin and coriander. Roast the tomatillos for 15 minutes on an upper rack in the oven, or until charred at edges and lightly browned. Place the baking sheet on a lower rack and leave the onions and garlic in oven to cook for an additional 10 more minutes.
Puree the tomatillos, onion, garlic and poblanos with 1 cup of stock, a small handful of cilantro and the lime juice. Transfer to a large pot along with the remaining stock and hominy; bring to a simmer over medium heat and cook for 15 minutes to combine the flavors.
Serve the posole topped with the radishes, avocados, scallions and a little more lime juice.