1. For the Sauce: Heat a large skillet over medium-high heat. Add the dried chiles and press down on them with a spatula, turning as needed until the color changes slightly, 3 to 5 minutes. Place the chiles in a heatproof bowl with enough boiling water to cover. Set aside for 30 minutes to rehydrate.

2. Heat the oil in a small skillet over medium heat. Add the onion and garlic and cook for 3 minutes, then transfer to a blender or food processor. Drain the chiles and add them to the blender, along with the remaining sauce ingredients. Process until smooth. Taste and adjust the seasonings. Set aside.

3. For the Burritos: Heat the oil in a large skillet over medium heat. Add the onion and cook until it begins to turn translucent, about 5 minutes. Add the poblano and cook 3 minutes. Add the mushrooms and garlic. Cook 3 to 5 minutes, until the mushrooms begin to soften. Add the beans, cumin, chili powder, oregano, red pepper flakes, tomato paste, lime juice, and nutritional yeast. Stir together, then add the spinach. Cook, stirring occasionally, about 5 minutes. Add a splash of broth or water if the mixture is too dry. Season with salt and pepper to taste.

4. Preheat the oven to 400°F. Lightly spray or oil a 9 x 13-inch baking pan. Fill each tortilla with 1/8 of the filling. Roll up and arrange in the baking pan. Repeat until all the burritos are filled. Pour the reserved sauce over the burritos and bake 15 to 20 minutes, until bubbly. Serve hot with toppings as desired.