Don't worry if you've never cooked with poblano before; they have a very mellow flavor. All of the heat in this dish comes from the salsa, so feel free to ramp that up if you like.
1 poblano chile, cut into strips
2 red bell peppers, cut into strips
1 small sweet potato, peeled and cut into 1/2-inch cubes (about 1 1/2 cups)
1 medium onion, halved and slivered
1 cup corn kernels, fresh or frozen
3 T olive oil
1½ tsp ground cumin
2 garlic cloves, minced
1 c salsa
2 oz baby spinach leaves (about 2 big handfuls)
5-6 corn tortillas
2½ cups shredded cheese
sour cream and thinly sliced scallions (green onions) for garnish, if desired
Preheat the oven to 425ºF.
Place poblanos, red bell peppers, sweet potato, and onion onto cookie sheet. Drizzle olive oil and sprinkle the cumin and minced garlic over top; toss to coat, and spread the vegetables evenly in the pan. Roast for 30–40 minutes, or until vegetables are tender and brown in spots. Stir every 10 minutes, and add the corn in the last 10–20 minutes. Remove pan from oven and reduce oven temperature to 350 degrees F.
Grease a deep 8" or 9" square baking pan. Spread 1/4 cup of salsa into the bottom of the baking pan. Add a layer of tortilla pieces, top with 1/3 of the vegetables, a handful of spinach, and 1/3 of the cheese. Make a second layer of tortilla, salsa, vegetables, spinach, and cheese. Repeat this order once more; cover with aluminum foil.
Bake for 20 minutes with the foil and 10 without, until cheese is melted and everything is heated through. Rest for 5 minutes before serving with sour cream and scallions.