Preheat the oven to 350°F (175°C).
In a mixing bowl, combine the shredded chicken, half of the shredded cheese, diced onions, garlic powder, cumin, salt, and pepper.
Spread 1/4 cup of the enchilada sauce on the bottom of a baking dish.
Spoon about 1/3 cup of the chicken mixture into the center of each tortilla.
Roll the tortillas tightly and place them seam-side down in the baking dish.
Pour the remaining enchilada sauce evenly over the top of the rolled tortillas.
Spread the sour cream over the sauce and sprinkle with the remaining cheese.
Cover the baking dish with foil and bake for 20 minutes.
Remove the foil and bake for another 10-15 minutes, or until the cheese is melted and bubbly.
Let the enchiladas cool for 5 minutes before serving.