Preheat the oven to 425°F (220°C) and line a baking sheet with parchment paper.
Slice the Italian bread horizontally, then cut into 4 pieces. Place cut-side up on the baking sheet.
In a bowl, mix butter, scallions (reserve some for garnish), garlic, mayonnaise, garlic powder, black pepper, sugar, and salt into a smooth paste.
Spread the garlic butter mixture evenly over the bread.
Mix mozzarella and Parmesan, then sprinkle evenly on top.
Bake the Cheesy Garlic Bread for about 15 minutes until the cheese is melted and golden.
Garnish with reserved scallions and serve warm.