Cook the Beef
In a skillet over medium heat, cook ground beef and diced onion until browned.
Drain excess grease, then stir in taco seasoning and Rotel. Remove from heat.
Mix the Casserole
In a large mixing bowl, combine hashbrowns, black beans, corn, cream of chicken soup, sour cream, and 1 cup of cheese.
Stir in the cooked beef mixture and season with salt and black pepper.
Slow Cook It
Grease the slow cooker with non-stick spray.
Pour the mixture into the slow cooker and spread evenly.
Cover and cook on low for 4–5 hours or high for 2–3 hours.
Add Cheese & Finish
Sprinkle the remaining 1 cup of cheese on top.
Cover and cook for another 15 minutes until the cheese is melted.