1) To prepare the salsa: Combine the tomatoes, spring onions, jalapeno, coriander, 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.
2) Preheat your oven to 180C/Gas 4. Spray a 23 by 33cm baking dish with nonstick cooking spray.
3) 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.
4) Place the tortillas on your work surface. Spoon about 125g 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 kitchen foil and bake until heated through, about 40 minutes.
5) Remove the foil and sprinkle the enchiladas with the remaining of the 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.