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