Cut sweet potato into ½" dice.
Stem poblano pepper, seed, and cut into ½" dice.
Halve and peel onion. Cut halves into ½" dice.
Coarsely chop cilantro (no need to stem).
Roast the Vegetables
Place sweet potato, poblano pepper, and onion on prepared baking sheet. Toss with 4 tsp. olive oil, chili powder, and a pinch of salt and pepper.
Roast until vegetables are tender, 25 minutes.
Make the Filling
Coarsely mash onion, sweet potato, poblano pepper, half the cilantro (reserve remaining for garnish), and ⅓ the enchilada sauce (reserve remaining for casserole dish and topping) in a mixing bowl.
Assemble and Bake Enchiladas
Pour 4 Tbsp. enchilada sauce (reserve remaining for topping enchiladas) into casserole dish, coating the bottom. (Use a dish large enough to fit six rolled tortillas.) Place one tortilla on a clean work surface. Add 1/6 the filling to tortilla, tightly roll up, and place in casserole dish, seam-side down.
Repeat for remaining five tortillas. Don't overfill tortillas. Make sure ends overlap and have a chance to seal while baking.
Pour remaining enchilada sauce over enchiladas and top with cheddar cheese.
Bake until cheese melts and begins to brown, 12-15 minutes.
Plate the Dish
Plate dish as pictured on front of card, garnishing with remaining cilantro, sour cream, and queso fresco. Bon appétit!