Preheat oven to 350 F. Dice onion (and any other preferred vegetables such as bell peppers) and sauté in a medium pan over medium heat. Cook until onions are translucent. Add spinach and cook until it's wilted. Add black beans and spices, and stir ingredients together. Season filling as preferred
To prepare tortillas, heat them in a skillet, 10 seconds per side. Then, dip them in Enchilada sauce. **Note- it is important to do this with WARM tortillas. Otherwise they will break as you try to fill and roll the enchiladas.
Fill corn tortillas with black bean and vegetable mixture, approximately three tablespoons. Roll to enclose, and place in a casserole dish, seam side down.
Top with additional enchilada sauce and shredded cheese. Bake at 350 degrees for 20 minuets. Garnish with sour cream.