Mix the black beans, corn, bell pepper, cumin and salt in a bowl.
Spread 1/2 cup enchilada sauce over the bottom of a greased 6-quart slow cooker.
Arrange four tortillas over the sauce, tearing them as needed to cover the bottom with minimal overlap.
Layer on half of the bean mixture, 3/4 cup cheese and 3/4 cup sauce, then repeat with four more tortillas and the remaining bean mixture.
Finish with the last four tortillas, remaining sauce and remaining cheese.
Cover and cook on low until the center is hot and the peppers are tender, 3 to 3 1/2 hours.
Turn off the cooker, uncover and rest the casserole for 20 minutes before scooping.