Preheat the oven to 400 degrees F. Put 1/4 cup red enchilada sauce on the bottom of a 13-by-9-inch baking dish.
Heat the olive oil over medium-high heat in a large skillet. Add the garlic, onions and jalapeño and cook until the onions become translucent and the garlic is fragrant, about 2 minutes.
Add the cubed sweet potatoes, diced tomatoes, black beans, cilantro, cumin, chili powder, salt and pepper to taste and 1/4 cup water. Cover and cook over medium-low heat, stirring occasionally, until the sweet potatoes are tender, about 10 minutes.
Place a generous 1/3 cup filling in the center of each tortilla, roll up and place in the baking dish seam-side down.
Top with the remaining 3/4 cup enchilada sauce and the cheese. Bake, covered with foil, until the enchiladas are hot and the cheese is melted, about 10 minutes. Top with more cilantro and serve with sour cream if desired.
Red Enchilada Sauce:
In a medium saucepan over medium-low heat, add the oil and saute the garlic until it is fragrant, about 30 seconds. Add the tomato sauce, chicken broth, chile powder, cumin, chipotle chiles and some salt and pepper. Bring to a boil. Reduce the heat to low and simmer until slightly thickened, for 5 to 7 minutes. Set aside until ready to use.