Preheat oven to 350ºF (177ºC). Spray a 9X13 inch baking dish with nonstick cooking spray, or butter dish with about 1 tablespoon of butter; set aside.
In a 12-inch skillet, add ground beef (1 pound) and sprinkle with cajun seasoning (1 teaspoon) and (1/2 teaspoon) black pepper. Cook over medium-high heat and crumble until the beef is cooked and there is no longer any pink in the beef.
Add the diced onion (1 cup) and red bell pepper (1), to the skillet and sauté until the vegetables are softened, 10-12 minutes. Add minced garlic (1 tablespoon) and continue to sauté stirring constantly, until the garlic is fragrant, about 1 minute.
Arrange 1 layer of the sliced potatoes at the bottom of the prepared dish. Season the layer of potatoes with (1/2 teaspoon) salt and (1/4 teaspoon) pepper to taste. Sprinkle 1 cup mozzarella and 1/2 cup of cheddar over the layer of potatoes. Repeat for the second layer of potatoes, seasoning, and cheese.
Arrange the ground beef and vegetable mixture in a layer over the potatoes.
In a medium mixing bowl, stir together the cream of chicken soup (1 can), cream of potato soup (1 can), milk (1/2 cup), sour cream (1/4 cup), and Worcestershire sauce (2 teaspoons). Pour the mixture over the beef and vegetables, spreading it out evenly.
Cover tightly with aluminum foil and bake in the preheated oven for 1 ½ hours.
Remove from the oven, take off the foil, and sprinkle the fried onions (3 ounces) on top. Place under a broiler for a few minutes to brown.
Let the casserole sit for 7-10 minutes. Garnish with sliced green onions (1/4 cup) or chopped fresh parsley (2 tablespoons). Slice, serve, and enjoy!