Preheat the oven to 401º F (205° C). Line a big baking sheet with parchment paper.
In a medium bowl add the butter, garlic, parsley and parmesan and mix with a spoon. Season with salt and black pepper to taste.
Slice the baguette into 2.5 cm pieces aproximately, not cutting all the way, to be able to stuff the bread with our ingredients. Place the baguette on top of a big piece of aluminium foil.
Using a kitchen brush or spoon, spread the butter mixture in between each slice, so the baguette is well impregnated.
Wrap the baguette with the aluminium foil making sure to cover it entirely and place it on the baking sheet.
Bake the baguette for 15 minutes. Take it out of the oven and take off the foil, but only on the top. If you want to add the mozzarella cheese, now is the time. Place it in the middle of each slice using a spoon.
Put the baguette back in the oven and bake again for 5 minutes until slightly golden brown and crisp.
Once ready, cut the garlic bread with a bread knife and serve while still hot.