To prepare the salsa: Combine the tomatoes, scallions, jalapeno, cilantro, and lime juice in a mixing bowl. Add a healthy pinch of salt and set aside at room temperature until ready to cook the enchiladas.
Preheat your oven to 350 degrees F. Spray a 9 by 13-inch baking dish with nonstick cooking spray.
To prepare the enchiladas: Place the shredded chicken in a large bowl. Add half of the grated cheese, sour cream, and onion; season with salt and pepper. Mix well to combine.
Place the tortillas on your work surface. Spoon about 1 cup of the chicken mixture across the center of each tortilla. Roll them up to close and place, seam side down, in the prepared baking dish. Pour the salsa over the tortillas. Cover with aluminum foil and bake until heated through, about 40 minutes.
Remove the foil and sprinkle the enchiladas with the remaining 1 cup of grated cheese. Return the baking dish to the oven until the cheese is melted and edges of the tortillas are just beginning to get crisp, 5 to 8 minutes. Serve hot.