Preheat the oven to 400° F and line a large baking sheet with parchment paper.
Slice the sweet potatoes in half lengthwise, rub the cut sides with olive oil, and sprinkle with a pinch of salt. Place potatoes cut-side down on the baking sheet and roast until very tender and easily pierced with a fork, about 30-40 minutes depending on the size. *Leave the oven on to bake the enchiladas shortly.
Meanwhile, pour ½ cup of red enchilada sauce into a 9"x13" baking dish to lightly cover the bottom. Set aside.
Make the filling. In a medium mixing bowl, add the black beans, 1 cup of Monterey Jack cheese, chipotle chile in adobo, cumin, garlic, chili powder, paprika, salt, pepper, lime juice, and soy sauce.
When the sweet potatoes are cool enough to handle, scoop the soft flesh out of the skins with a spoon and lightly mash with a fork so that it's mostly creamy but with a bit of texture.
Stir the mashed sweet potato into the bowl of filling, and season to taste with additional salt and pepper. The filling should taste delicious on its own.
Wrap tortillas in a damp paper towel or kitchen towel and microwave for about 45 seconds, until they're warm and pliable. Warm tortillas roll easily and are much less likely to split or tear once they're filled.
Lay one corn tortilla in the baking dish to lightly coat one side in sauce, then flip to coat the other side. Add about ¼ to ⅓ cup of filling down the center (depending on the size of your tortillas), roll it up, and place it seam-side down along one edge of the dish. Repeat with the remaining tortillas, adding more sauce as needed to keep them moist. If you have any filling left, tuck it along the sides of the enchiladas. *If you run out of room to sauce and roll tortillas in the baking dish, use a small plate to dip, fill, and roll them, then transfer to the baking dish.
Pour remaining enchilada sauce evenly over the top of the enchiladas, and sprinkle with ½ cup Monterey Jack cheese and ½ cup cheddar cheese. Bake for 25-30 minutes, until cheese is lightly golden and bubbly on the edges.
Garnish with avocado and cilantro. Serve immediately.