Preheat the oven to 350°F.

In a skillet over medium heat, sauté the chopped onions until soft and translucent.

Stir in the shredded chicken, taco seasoning, diced tomatoes with green chilies, and half of the cream of chicken soup. Cook on low heat until the ingredients are well combined.

Distribute the chicken mixture evenly among the tortillas, spooning it down the center of each one.

Roll up the tortillas and place them seam side down in a 9x13-inch baking dish.

In a mixing bowl, whisk together the remaining cream of chicken soup, sour cream, and milk until smooth.

Pour the sour cream mixture over the enchiladas in the dish, making sure to cover them completely.

Sprinkle the shredded cheese over the top of the enchiladas.

Bake in the preheated oven for 20 minutes, or until the enchiladas are heated through and the cheese is melted and bubbly.