Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish with butter or cooking spray.
Place a large skillet over medium-high heat. Add the ground beef and diced onions, cooking until the beef is browned and the onions are translucent.
Drain any excess fat from the skillet to prevent the casserole from becoming greasy.
Stir in the minced garlic, Worcestershire sauce, sugar-free ketchup, mustard, salt, and pepper. Cook for 1-2 minutes until fragrant, then remove from heat.
Transfer the seasoned beef mixture to the prepared baking dish and spread it into an even layer.
Sprinkle the crumbled bacon and 1 cup of the shredded cheddar cheese evenly over the top of the beef.
In a medium mixing bowl, whisk together the eggs and heavy whipping cream until the mixture is uniform and slightly frothy.
Pour the egg and cream mixture slowly over the beef and cheese, ensuring it reaches all corners of the dish.
Top the casserole with the remaining 1 cup of shredded cheddar cheese.
Bake for 30 to 35 minutes, or until the cheese is golden brown and bubbly and the egg mixture is fully set in the center.
Allow the casserole to rest for 5 to 10 minutes before slicing. Garnish with dill pickle slices prior to serving.