Begin by making the enchilada sauce: Light a grill and set it on high. Place the chiles on the grill and cook for several minutes until the skins turn black and begin to blister. Remove and allow to cool. Remove the papery leaves from the tomatillos and add those to the grill. Cook 1-2 minutes or until they just begin to soften. Remove and let cool. While the grill is on, grill the pork chop and the corn (keep the corn in the husk and cook over indirect heat — if your grill has an upper shelf that works well).
Remove the stem and seed core from the chiles. Use a knife to scrape away the outermost layer of skin (it will be very thin a film-like and should peel off fairly easily). Chop.
Use a blender or food processor to puree the tomatillos. Add the tomatillo puree, chopped chiles, broth, onion, garlic, oregano, salt, and pepper to a saucepan and bring to a boil. Reduce heat and let simmer for 10 minutes. Whisk in the cornstarch and let simmer another 10 minutes, or until the sauce is thickened.
While the sauce is cooking, use two forks to shred the grilled pork chop.
Assemble the enchiladas: Ladle a little bit of the enchilada sauce into the bottom of a large baking dish. Place two tortillas in the dish, side by side. Top each tortilla with 1/4 of each the pork, black beans, and pineapple. Spoon on a little bit of the sauce and add a little shredded cheese. Top with another tortilla and repeat to make a second layer. Top each stack with third tortillas. Cover with the remaining sauce and top with the rest of the cheese.
Bake at 450 for 10 minutes, or until the cheese had melted and the sauce has thickened.
While the enchiladas bake, prepare the salsa: Cut the corn away from the cob. In a large bowl, combine the corn, avocado, tomato, red onion, lime juice, and cilantro. Season to taste with salt.
Serve the enchilada stacks topped with the salsa.