Preheat your oven to 350°F (175°C) and line a baking sheet with foil or parchment paper.

Slice the wide French bread in half lengthwise and lay the halves cut-side up on the prepared baking sheet.

Mix the softened unsalted butter with garlic salt until well combined and spread it on the cut sides of the bread.

In a large skillet over medium-high heat, cook the ground beef and diced onion for about 8-10 minutes until browned.

Reduce heat to medium-low and add garlic powder, yellow mustard, ketchup, salt, black pepper, Worcestershire sauce, brown sugar, and water to the skillet, simmer for 2-3 minutes.

Evenly divide the savory beef mixture across the cut sides of the garlic bread and sprinkle with mozzarella and cheddar cheese.

Bake for 12-14 minutes until the cheese is melted and bubbly.

Let cool for 1-2 minutes, slice into portions, and serve garnished with chopped parsley.