Preheat the oven to 350 and grease a large baking dish
To Make the Enchilada Filling: Place a medium skillet over medium heat with a drizzle of oil. When the oil is hot, add the spinach and cook, stirring occasionally, until wilted. In a large bowl, combine the black beans, corn, spinach, green onions, cilantro, garlic, cumin, and 2 cups of shredded cheese.
To Make The Sauce: In a medium bowl, mix together the tomato sauce, olive oil, garlic, chili powder, cumin, and salt. Set aside.
To Assemble The Enchiladas: Pour half of the enchilada sauce in the base of the baking dish, For each enchilada, place the enchilada filling in the centre of each tortilla, roll the tortilla up, and place it in the baking dish.
Once the enchiladas are all lined up in the baking dish, pour the rest of the sauce over the enchiladas. Sprinkle with the remaining cup of shredded cheese. Place in the oven and bake for 20 minutes.