Spray your slow cooker with nonstick cooking spray. Place chicken breasts in the bottom of the slow cooker in a single layer.
Add enchilada sauce, fire-roasted tomatoes, green chiles, and taco seasoning. Stir gently to combine the sauce ingredients.
Cover and cook on High for 3-4 hours or on Low for 4-6 hours. You can stretch cooking time to 6-8 hours on Low if needed. Chicken is done when tender and reaches 165°F internal temperature.
Once chicken is tender, remove it from the slow cooker and shred with two forks or use a stand mixer with paddle attachment for faster shredding.
Return shredded chicken to the slow cooker. Stir in half of the shredded cheese, all the black beans, and corn.
Add the sliced tortillas and gently mix everything together. If using, stir in cream cheese until melted.
Flatten the mixture slightly, then sprinkle the remaining cheese over the top.
Cover and cook an additional 20-30 minutes on Low until cheese is melted and everything is heated through.
Let rest for 5 minutes. Garnish with chopped cilantro and serve hot with optional toppings.