Roasted Vegetable Enchilada Bake

Preheat the oven to 400 degrees F.  Heat the oil in a large, deep, nonstick skillet over medium-high heat. Add the onion and ¼ cup salsa, and sauté until the onion is softened, about 8 minutes. Add the mushrooms and pepper and sauté until softened, about another 5 minutes. Stir in the spinach, and toss until just wilted, about 1 minute. Add the beans, cilantro, oregano, cumin, and salt, and sauté until fully combined and heated through, about 1 minute. Adjust seasoning.  Spread ½ cup salsa into a 9x13-inch baking dish. Arrange 6 tortillas to cover the bottom of the dish. Evenly top with half of the vegetable mixture. Arrange the remaining 6 tortillas on top. Sprinkle with ¼ cup salsa. Evenly top with remaining vegetable mixture. Sprinkle with the cheese. Bake until fully cooked through and the cheese is melted, about 20 minutes. Sprinkle with remaining ¼ cup salsa.  Cut the casserole into 6 portions, and serve.