Preheat your oven to 350 degrees and grease a large lasagna pan (a little larger than a 9-inch by 13-inch baking pan) with cooking spray. Set aside.
Heat a large skillet over medium heat and add the olive oil.
Add the onion and garlic to the hot pan, along with the salt and pepper.
Sautee the onion and garlic until the onion is translucent and the garlic is fragrant. Add the sweet potatoes and the black beans, and continue to cook for a few minutes in the onion and garlic mixture.
Add the 1 cup of enchilada sauce along with the vegetable stock and stir together well.
Continue to cook for about 10-15 minutes, or until the sauce has thickened a bit and the sweet potatoes are just fork tender.
Turn off the heat and set the filling aside.
Ladle about 3/4 cup of enchilada sauce into the bottom of the prepared baking pan and spread it out with a spoon or rubber spatula. Use my Easy Homemade Enchilada Sauce for this recipe!
Place about 1 big spoonful of the filling into each of the 10 tortillas and add a small handful of cheese on top of each (reserve about 1/2 cup of the shredded cheese for topping later).
Roll the enchiladas leaving the ends open and place them seam-side down into the baking pan, nestling them into the enchilada sauce on the bottom of the pan.
Roll all 10, placing them side by side in the pan.
Top them with the remaining 3/4 cups of enchilada sauce, and then the 1/2 cup shredded cheese and bake at 350 degrees for about 18-20 minutes or until the cheese bubbles and the edges of the enchiladas begin to turn a slight golden brown.
Let them rest for about 5 minutes before serving with a dollop of sour cream, some chopped avocado, tomatoes and cilantro.