Preheat oven to 375F
Cook ground beef and onion in a skillet over medium heat and season with salt, pepper, and Worcestershire sauce
Mix all Big Mac sauce ingredients together in a bowl
In a casserole dish, add ground beef and chopped pickles on top
Drizzle half of Big Mac sauce on top followed by the mozzarella and cheddar cheese
Bake for 20 mins, or until the cheese is melted and bubbly
Drizzle on remaining sauce, more pickles, and top with sesame seeds
