First, season the chicken generously with big pinches of salt, black pepper and garlic powder. Then get out a large slow cooker and combine the seasoned chicken, sun-dried tomatoes, mushrooms, spinach and alfredo sauce in it. Turn it on to low and let it all cook for 4 hours. When the time is almost up, get a large pot of water on to boil. Salt it generously, then cook the spaghetti until tender for about 8 minutes. Turn off the slow cooker at this point and remove the lid. Drain the spaghetti and transfer it right into the slow cooker with the sauce. Toss it all together thoroughly, then serve immediately in pretty bowls!