In a slow cooker, combine the chicken, enchilada sauce, onion, green chilies, garlic powder, and 1/2 teaspoon salt. Cook on low heat for 6-8 hours or on high for 4. Remove the chicken to a cutting board and use two forks to shred it. Return to the slow cooker and keep warm.
Preheat oven to 425 degrees F. Wash and dry the potatoes. Poke the potatoes all over with a fork then drizzle with olive oil to coat on all sides. Sprinkle with Kosher salt. Use tongs to transfer the potatoes directly to the rack in the oven. Bake until fork tender, about 45 minutes to 1 hour.
When the potatoes are done, remove them from the oven. Place a long slit down the center of each potato and use your fingers to pinch it together and get the potato to fan out. Spread with butter and sprinkle with salt and pepper, if desired. Top each potato with chicken, chopped avocado, cheese, sour cream, and cilantro.