Start by preheating your oven's broiler to high heat.
In a mixing bowl, combine mayonnaise, grated Parmesan cheese, and garlic powder, stirring until the mixture is thick and evenly blended.
Carefully slice the loaf of bread in half lengthwise and generously spread the mayonnaise mixture on the cut sides of both halves. Place them on a baking sheet.
Broil the bread in the oven for 2 to 5 minutes, keeping a close eye on them until the topping is bubbling and turns a lovely golden brown. Be sure to check regularly to prevent burning.
