Heat the oven to 375°F and line a rimmed baking sheet with aluminum foil; set aside.

Take the frozen garlic bread from the freezer so it can thaw while you make the Sloppy Joe filling.

Warm a large skillet over medium-high heat and add the butter. Once melted, add the chopped onion and cook until soft and translucent, about 3–4 minutes.

Add the ground beef to the skillet and cook, breaking it up with a spatula, until there is no pink remaining, about 5–6 minutes. Drain off any excess fat.

Reduce heat to medium-low, stir in the Sloppy Joe sauce, salt, and black pepper, and let the mixture simmer gently for about 5 minutes to blend flavors.

Unwrap the thawed garlic bread and separate the two halves using a knife if needed. Place both halves butter-side up on the prepared baking sheet.

Spread the Sloppy Joe mixture evenly across each half of the garlic loaf so both pieces are covered in a uniform layer.

Top each loaf with 1 cup of shredded Colby Jack, distributing the cheese evenly over the meat.

Bake in the preheated oven until the cheese has melted and is bubbly, about 15–18 minutes.

Let the loaves rest briefly, sprinkle with chopped parsley if desired, then slice into 2-inch breadsticks and serve warm.