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