Prepare the Meat: In a large skillet, brown the ground beef over medium-high heat. Drain off any excess grease. Stir in the taco seasoning and water. Bring to a simmer and cook for 5 minutes, or until the liquid is mostly absorbed.

Make the Cream Cheese Mixture: In a mixing bowl, combine the softened cream cheese and sour cream. Mix until smooth and creamy.

Layer the Casserole: Spread a thin layer of the ground beef mixture on the bottom of the slow cooker. Top with a layer of tortillas (cut or tear them to fit). Spread half of the cream cheese mixture over the tortillas. Sprinkle with half of the black beans, corn, and diced tomatoes and green chilies. Top with half of the shredded cheddar cheese.

Repeat Layers: Repeat the layering process: ground beef mixture, tortillas, remaining cream cheese mixture, remaining black beans, corn, and diced tomatoes and green chilies, and remaining cheddar cheese.

Cook: Cover and cook on low for 3-4 hours, or on high for 1.5-2 hours, or until the cheese is melted and bubbly, and the tortillas are softened.

Rest: Let the casserole rest for 10-15 minutes before serving. This allows the flavors to meld and the casserole to set up slightly.

Serve: Top with your favorite taco toppings, such as shredded lettuce, diced tomatoes, sour cream, and guacamole.