Preheat oven to 350°F. Prepare a pie plate with a spritz of nonstick cooking spray.
Cook the ground beef in a skillet, breaking it up into smaller pieces with a spatula or wooden spoon, until it's completely browned, about 8-10 minutes.
Add to the skillet the diced onions, salt, pepper, and garlic powder. Continue cooking until onions are translucent, about 1-2 minutes. Stir in the Worcestershire sauce and mustard. Add the bacon bits if desired.
Remove the skillet from the heat and fold in 1 cup of the cheddar cheese. Spread the beef mixture evenly in the prepared pie plate.
In a medium mixing bowl, whisk together the eggs, mayonnaise, and cream. Pour this mixture evenly over the beef mixture, then sprinkle the remaining cheddar cheese on top.
Bake the casserole uncovered until it's hot throughout and the cheese is bubbly, about 25 minutes.
Remove from the oven and let the casserole rest for 3-5 minutes before slicing. Serve hot with optional burger toppings like low-sugar ketchup, mustard, and sliced pickles.