MAKE THE SPECIAL SAUCE. In a small bowl, mix the mayonnaise, ketchup, mustard and relish until well combined; transfer to a serving bowl until ready to use.

MAKE THE PULL-APART BREAD. Preheat the oven to 350-degrees and line a large baking sheet with aluminum foil.

Using a large serrated knife, cut 1-inch slices into the loaf, cutting ¾ of the way through.

Rotate the bread 180-degrees and cut 1-inch slices into the loaf, cutting ¾ of the way through, to create cubes.

In a larger skillet, warm the oil over medium-high heat.

Add the onions and sauté until softened, about 5 minutes

Add the meat and a generous pinch of salt and cook until browned, about 7 minutes.

Add 2 cups of the cheddar cheese and cook, stirring constantly, until the cheese has melted and the mixture is creamy, for 1 to 2 minutes.

Season with additional salt, if needed, to taste.

Working quickly, spoon the meat and cheese filling into all the crevices of the bread, carefully separating the cubes with your fingers.

Loosely cover with foil and bake until warmed through, about 15 minutes.

Sprinkle the remaining cheese evenly over the top and bake, uncovered, until the cheese has melted, about 7 minutes.

Serve immediately with Special Sauce.