Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish with cooking spray.

Season chicken breasts with salt and pepper. In a large pot, bring 4 cups of water to boil. Add chicken and cook for 15-18 minutes until internal temperature reaches 165°F.

While chicken cooks, heat olive oil in a skillet over medium heat. Sauté onion for 3-4 minutes until softened. Add garlic, cumin, and chili powder; cook 1 minute more.

Remove chicken from water and shred using two forks. Mix shredded chicken with sautéed onion mixture, sour cream, and 1 cup of cheese.

Warm corn tortillas in microwave for 30 seconds wrapped in damp paper towels to make them pliable. Spread 1/2 cup enchilada sauce in bottom of baking dish.

Fill each tortilla with about 1/3 cup chicken mixture. Roll tightly and place seam-side down in baking dish. Pour remaining sauce over top and sprinkle with remaining 2 cups cheese.