Season the pork

In a large bowl, toss the pork with salt, pepper, cumin, sugar, chili powder, and garlic powder. Let sit at room temperature 1 hour, or refrigerate for up to 24 hours.

Make the pickled onion

In a medium bowl, toss the onion with the sugar and salt, and let sit for 10 minutes. Toss with the vinegar, cover, and refrigerate for up to 2 days.

Make the stew

Preheat the oven to 425°F. Line a baking sheet with foil. Place chiles, cut- side down, on baking sheet. Roast until skins are charred, about 20 minutes. Wrap peppers in the foil, and let stand 20 to 30 minutes or until cool enough to handle. Peel off skin.

For the broth, in a blender, combine the peppers, broth, 1/2 cup cilantro, the scallions, and cumin until smooth.

Sprinkle the pork with flour and toss to coat. Heat a large heavy Dutch oven over medium-high heat. Add the oil, and when shimmering, add half of the pork in an even layer. Cook, undisturbed, until browned around the edges and pork easily releases when lifted with tongs, about 2 minutes. Reduce the heat to medium. Flip, and cook until browned, about 2 minutes. Transfer to a plate. Cook the remaining pork; transfer to the plate.

Add the puree to the pot, and bring to a boil. Return the pork and any accumulated juices to the pot, along with the corn. Reduce the to medium low and cook, stirring occasionally, until the pork is cooked through and the broth thickens, about 15 minutes. Add the lime juice, and season generously with salt and black pepper.

Serve, topped with the remaining 1/2 cup cilantro, the onion, and queso fresco.