Instructions

1. Preheat the oven to 400 degrees Fahrenheit. Lightly grease a 9 by 13-inch pan with olive oil or cooking spray. 
2. In a medium Dutch oven, warm the olive oil over medium heat. Add the onion, bell pepper and ½ teaspoon salt. Cook until the onion and pepper are tender, stirring occasionally, about 5 to 6 minutes. 
3. Add the mushrooms and remaining ¼ teaspoon salt. Continue cooking for 6 to 9 minutes, stirring often, until the mushrooms start to caramelize and stick to the base of the pan. 
4. Add the spinach in big handfuls, stirring after each. Cook until the spinach is wilted, about 2 to 4 minutes. 
5. Add the garlic and cumin and cook until fragrant, about 30 seconds to 1 minute. Remove the pot from the heat and stir in the black beans, followed by the cheese. Season to taste with salt and pepper as desired. Set the mixture aside to rest for a few minutes.
6. Meanwhile, spread the tortillas across a large, rimmed baking sheet and bake just until they are warm and pliable, about two minutes. Stack the tortillas and wrap them in a clean tea towel to keep them warm.
7. To assemble the enchiladas, pour 1/3 cup of each sauce into the base of the prepared baking dish (half on one side, half on the other). Gently spread each sauce over each half of the baking dish.
8. Working with one tortilla at a time, spread about ⅓ cup filling down the center of a tortilla. Roll the tortilla around the filling, then place them snugly side-by-side in the baking dish with the seams down. Spread the remaining ⅔ cup red sauce over one-half of the tortillas (to match the red sauce in the base of the dish), and the remaining green sauce over the other half. 
9. Bake, uncovered, on the middle rack for 20 to 22 minutes, until the sauce is bubbling around the edges and the top of the enchiladas are turning a bit more matte than glossy. Garnish as desired, and serve.