Spray the slow cooker liner with nonstick cooking spray and place the chicken breasts in an even layer in the bottom of the crockpot.
Sprinkle the taco seasoning evenly over the chicken breasts.
Distribute the cream cheese (cut into chunks) and the queso cheese (cubed or in chunks) on top of the seasoned chicken.
Pour the Rotel (diced tomatoes and green chiles) over the cheeses and chicken.
Cover and cook on HIGH for 3 hours or on LOW for 7 hours, until the chicken is very tender and cooked through.
Remove the lid and shred the chicken directly in the crockpot using two forks, then stir everything together until combined and creamy.
Serve hot as a dip or use as a filling for tacos, and top with sliced green onion tops if desired.