Bring a pan sprayed with nonstick spray to medium heat on the stove. Add onion and, stirring occasionally, cook until it begins to brown, about 2 minutes. Transfer to a medium bowl.
Add pumpkin, taco sauce, and taco seasoning to the bowl. Mix well. If you like, season to taste with salt and pepper. Set aside.
Spray a small baking dish with nonstick spray and set aside. Warm tortillas slightly in the microwave.
Lay tortillas flat on a clean, dry surface. Spread 2 tablespoons enchilada sauce onto each one. Place a half-slice of cheese in the center of each tortilla. Evenly distribute the pumpkin mixture between the centers of the tortillas.
Wrap tortillas up tightly and place them in the baking dish with the seam sides down. Cover with remaining 1/2 cup enchilada sauce.
Bake in the oven for about 8 minutes, until enchiladas are hot. Carefully remove dish from the oven, and sprinkle enchiladas with shredded cheese.
Return to the oven and bake for another 5 minutes, or until the cheese has melted. Plate those babies and, if you like, top with sour cream and/or scallions. Enjoy!