Preheat oven to 400 degrees F. Line a rimmed baking sheet with parchment or foil.
Char the poblano directly over a gas flame or under a broiler, turning until skin is blistered and blackened on all sides. Transfer to a bowl, cover, and steam 5 minutes. Peel away most of the skin, remove stem and seeds, and slice into thin strips.
In a small bowl, toss shredded chicken with salsa and taco seasoning if using. Chicken should be lightly coated, not wet.
Spread chips in a single even layer on the prepared baking sheet. Sprinkle half the cheese evenly over the chips.
Distribute chicken evenly over the cheese layer. Add poblano strips. Finish with the remaining cheese.
Bake 10 to 12 minutes until cheese is fully melted and chip edges are lightly crisped.
Remove from oven and immediately top with pickled jalapenos and sliced scallions. Serve hot with sour cream and guacamole on the side.