In a large skillet over medium-high heat, brown the lean ground beef with the chopped yellow onion and diced green bell pepper. Cook until the beef is no longer pink and the vegetables are softened, about 7-10 minutes. This initial step develops a deep flavor base and helps prevent the casserole from becoming greasy. The process of browning adds significant depth to the dish. Once cooked, carefully drain any excess fat from the skillet.

Arrange the quartered red potatoes in an even layer at the bottom of a 6-quart (or larger) slow cooker. Placing them at the bottom helps ensure they cook thoroughly, as they take the longest. Sprinkle the frozen sweet corn evenly over the potatoes.

Add the browned ground beef mixture from the skillet over the corn layer. Next, distribute the rinsed and drained kidney beans evenly on top of the beef mixture. These layers create a satisfying texture throughout the casserole.

In a separate medium bowl, combine the undrained Rotel diced tomatoes with green chilies, the undrained fire-roasted diced tomatoes, and the beef broth. Stir in the minced garlic, chili powder, smoked paprika, black pepper, sea salt, Worcestershire sauce, and the optional cayenne pepper or hot sauce. Mix these ingredients thoroughly to ensure all the spices are well-distributed and the sauce is uniform.

Carefully pour the tomato and spice mixture over all the ingredients in the slow cooker. Gently stir to ensure everything is moistened and partially submerged in the liquid, which will help cook the potatoes and meld all the flavors together during the slow cooking process.

Cover the slow cooker with its lid and cook on LOW for 6 hours or on HIGH for 4 hours. The casserole is ready when the potatoes are fork-tender and the flavors have fully melded together. Avoid frequently lifting the lid, as this releases heat and prolongs cooking time.

Once the casserole is cooked, open the slow cooker and sprinkle the shredded sharp cheddar cheese evenly over the top. Replace the lid and allow it to cook for an additional 10-15 minutes, or until the cheese is beautifully melted, gooey, and bubbly. This creates a delicious, cheesy crust.

Turn off the slow cooker and let the casserole rest for 5-10 minutes before serving. This brief resting period allows the sauce to thicken slightly. Serve hot as a complete, satisfying meal, perhaps with a side of cornbread or a simple green salad.