Heat the oven to 425°F and line an 18-by-13-inch rimmed sheet pan with foil. Toss poblano, onion and corn with oil, cumin and salt and roast for 15 minutes, stirring once.
Transfer roasted vegetables to a bowl and fold in black beans. Reduce the oven to 400°F.
Spread half the chips on the same pan, scatter with half the bean mixture and half the cheese, then repeat with the remaining chips, beans and cheese in a loose, shallow layer.
Bake for 8 to 10 minutes until cheese is melted and beans are hot throughout, watching the exposed chips for darkening.
Spoon salsa and sour cream over the tray in small amounts and serve immediately in 4 portions.