Turn the oven to broil. Line a baking sheet with parchment paper.
Combine the mayonnaise, mozzarella, chilies, and dry rub in a bowl.
Spread the mixture onto the bread. Place both halves on the baking sheet and bake for 6 minutes at 350°F(175°C) then move to broil for about 5-7 minutes until the cheese is bubbly and melted.
Let rest for about 3 minutes. Then slice, garnish with chopped parsley, if using, and serve hot.
Notes
If your loaf of French bread is large you might want to make a double batch of the topping.