Start by gathering all your ingredients. Make sure the mozzarella cheese is sliced and the pepperoni is ready to go.
In a small bowl, combine the mayonnaise with a pinch of salt and pepper, if desired.
Spread the butter on one side of each slice of Dave's Killer 21 Power Seed Bread.
On the unbuttered side of one slice of bread, spread the mayonnaise mixture. Layer on one slice of mozzarella cheese, followed by the pepperoni slices, and then the pizza sauce. Top with the second slice of mozzarella cheese before covering it with the other slice of bread, buttered side up.
Place your skillet or griddle over medium heat. Once hot, carefully place your assembled sandwich onto the skillet.
Cook the sandwich for about 3-4 minutes, or until the bottom is golden brown. Using a spatula, carefully flip the sandwich to grill the other side. Cook for another 3-4 minutes until the cheese is melted and the bread is golden.
Once both sides are beautifully toasted and the cheese is deliciously gooey, remove the sandwich from the skillet. Allow it to cool for a minute before slicing it in half. Serve with extra pizza sauce for dipping, if desired.