Preheat the oven to 425 degrees and lightly oil a large rimmed cookie sheet.
Place poblano, bell peppers, cauliflower, sweet potato, potatoes, onion, and corn on the cookie sheet. Drizzle with the olive oil and sprinkle the cumin, garlic, and salt and pepper on top. Toss to coat. Spread the vegetables out in the pan in a single layer.
Roast for 30 minutes or until the vegetables are tender and beginning to brown. Stir or shake the pan every 10 minutes for even roasting. Remove the pan from the oven and reduce heat to 350 degrees. Good luck not eating the roasted vegetables right from the pan at this point.
Prepare an 8x8x2 or 9x9x2 baking dish with nonstick spray.
In a small bowl, stir the cilantro into the salsa. Spread 1/4 cup of the salsa on the bottom of the baking dish. Add a layer of torn tortilla pieces, then a layer of vegetables, a layer of spinach, and top with a layer of cheese. Repeat the layers two times, ending with the cheese.
Cover with foil and bake for 20 minutes. Remove foil and bake for another 10 minutes or until the cheese is melted and everything is heated through.
Let sit for 5 minutes and then cut into squares. Serve with sour cream and scallions, if desired.