cilantro, for serving (optional) (I also added a little shredded cheddar-jack, black beans and scallion on top)
Put chicken, soup, and salsa in slow cooker. Sprinkle taco seasoning over everything. Cook on low for 6 hours. If shredding the chicken, pull the breasts out and shred; return back to slow cooker. Stir in sour cream and heat just until everything is combined.