Preheat oven to 350°F (180°C) and line a baking sheet with parchment paper or foil.
Halve the ciabatta loaf lengthwise, then evenly spread the softened butter over each cut side. Sprinkle with garlic powder, salt, and pepper, then set aside.
In a skillet or Dutch oven set over medium-high heat, warm the olive oil. Add the ground beef and break it apart with a wooden spoon, cooking until browned with no remaining pink. Drain any excess fat if necessary.
Stir in the diced onion and cook until it becomes translucent. Incorporate the minced garlic and sauté briefly for 30 seconds.
Pour in the ketchup, water, brown sugar, yellow mustard, Worcestershire sauce, and season with salt and pepper. Mix thoroughly to combine. Cover the skillet with a lid, reduce heat, and allow the mixture to simmer for 20–30 minutes, or until it thickens to your preference. Taste and adjust seasonings if needed.
Evenly distribute the Sloppy Joe mixture across the buttered ciabatta halves. Top with the shredded mozzarella and cheddar cheeses.
Bake in the preheated oven for approximately 10 minutes, or until the cheese is melted and the edges of the bread are golden brown. Remove, slice, and serve, garnished with chopped parsley if desired.