Preheat the oven to 200 degrees Celsius/ 400 degrees Fahrenheit.
Saute: Finely chop the onion. Heat the oil in a saucepan and cook the onions for about 2 minutes or until translucent. Grate the garlic and add it to the pan together with the chili. Stir for one minute.
Sauce: Blend the canned tomatoes in a blender or with an immersion blender. Pour into the pan, add the sugar, dried oregano, and salt and cook on medium heat for 5 minutes. Cover the pan partially if it starts to splutter. Stir occasionally. Remove the tomato sauce from the heat and let cool for 5 minutes. Stir in the sour cream and the chopped coriander.
Prepare ingredients: In the meantime, shred the chicken and finely slice the scallions. Grate the cheese.
Heat tortillas: Heat a large pan without adding any oil. Heat one tortilla at a time in the pan and until softer and pliable, about 10 seconds on each side. Repeat with the rest of the tortillas.
Assemble: Place 2-3 tablespoons of the tomato and sour cream sauce to a casserole dish of about 25x20 cm/ 10x8 inches, the bottom of the pan should be covered with a thin layer of sauce.
Fill enchiladas: Smear each tortilla with about 1 tablespoon of the sauce. Divide the shredded chicken meat and the scallions between the tortillas. Sprinkle the filling with just a little bit of the grated cheese.
Roll the tortillas and place them in the casserole dish. Pour the remaining tomato and sour cream sauce over the enchiladas and sprinkle everything with the remaining grated cheese.
Bake enchiladas for only 10-15 minutes. The cheese should be melted, and the enchiladas should be heated through.
Leave the enchiladas to rest for about 5 minutes, then serve immediately as suggested above.