Preheat the oven to 425°F.
Dice bell peppers; peel sweet potato and cut into 1/2-inch cubes (about 1 1/2 cups worth); mince garlic and onion.
Place bell peppers, sweet potato, onion, and corn onto a cookie sheet, and drizzle with olive oil; sprinkle cumin and minced garlic over top.
Add a generous pinch or two of salt and pepper, then mix everything together and spread into an even layer in the pan.
Roast for 30-40 minutes until vegetables are tender and begin to brown. Stir or shake pan every 10 minutes for even roasting.
Remove pan from oven and reduce oven temperature to 350° F. Spray an 8x8 or 9x9 inch baking pan with cooking spray.
Chop cilantro and mix together with salsa.
Spread 1/4 of the salsa mixture into bottom of the prepared pan.
Cut tortillas in half and add a layer to the pan, completely covering the salsa. Drain and rinse beans.
Top tortilla pieces with 1/3 of the vegetables, the beans, a handful of spinach, and 1/3 of the cheese.
Make a second layer of tortilla pieces, then add more salsa, vegetables, spinach, and cheese.
Top with a final layer of tortillas, salsa, vegetables, and cheese, then cover with aluminum foil.
Bake for 20 minutes, then remove the foil and bake another 10 minutes until cheese is golden and everything is heated through.
Let set for 5 minutes, then cut into squares.
Top each serving with sour cream and a sprinkle of sliced green onions.