Bring a skillet 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 bowl.
Add pumpkin, taco sauce, and taco seasoning to the bowl. Mix well. If you like, season with salt and pepper, to taste. Set aside.
Spray a baking pan with nonstick spray and set aside.
Place tortillas on a microwave-safe plate. Warm slightly in the microwave, about 15 seconds.
Lay tortillas flat, side by side. 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 pan with the seam sides down. Cover with remaining 1/2 cup enchilada sauce.
Bake in the oven until enchiladas are hot, about 8 minutes.
Carefully remove pan from the oven, and sprinkle enchiladas with shredded cheese.
Return to the oven and bake until the cheese has melted, about 5 minutes. Plate those babies and, if you like, top with sour cream and/or scallions. Enjoy!