Place the chicken breasts in the crockpot and sprinkle the taco seasoning evenly over them. Pour the salsa on top, then add the black beans and corn. Stir gently to combine.
Cover the crockpot and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is cooked through and easily shreds with a fork.
Once the chicken is cooked, shred it in the crockpot using two forks and mix it with the other ingredients.
Preheat your oven to 350°F. On a large baking sheet, spread half of the tortilla chips in an even layer. Top with half of the chicken mixture, then sprinkle with half of the cheddar cheese. Repeat the layers with the remaining chips, chicken mixture, and cheese.
Bake in the preheated oven for 10-15 minutes, or until the cheese is melted and bubbly.
Remove from the oven and top with diced tomatoes, jalapeños (if using), and fresh cilantro. Serve immediately with sour cream on the side.