Toss the squash, 2 tablespoons vegetable oil, 1/2 teaspoon each of chili powder and cumin, the salt and several grinds of pepper on a rimmed baking sheet. Roast, tossing once, until browned and tender, but not falling apart, 25 to 30 minutes.
Meanwhile, heat the remaining 2 tablespoons vegetable oil in a large skillet over a medium heat. Add the onion and cook, stirring, until lightly browned and tender, about 10 minutes. Stir in the black beans and the remaining 1/4 teaspoon each of cumin and chili powder. Cook until the beans are heated through and well combined, about 2 minutes. Remove from the skillet and set aside on a plate. Pour the enchilada sauce into the skillet, then reduce the heat to low and warm through.
One at a time, hold the tortillas over a stovetop burner set on a medium heat to brown slightly, about 30 seconds per side. Set aside.
Pour 2 cups of the enchilada sauce into a 9-by-13-inch baking dish. To assemble the enchiladas, dip a tortilla into the remaining sauce, then lay on a plate. Sprinkle some cheese down the middle, followed by some of the bean mixture and finally some of the roasted squash. Roll it up tightly, then place seam-side down in the baking dish. Repeat with the rest of the tortillas. If you have any extra pieces of squash or the bean mixture, tuck them in between the enchiladas. Be sure to save a little cheese for the topping!
Pour the rest of the sauce over the enchiladas, then top with the remaining cheese. Add a final sprinkling of chili powder, then bake until hot and bubbly, 20 to 30 minutes. Let sit for 15 to 20 minutes before serving. Top with the cilantro.