Thaw the pizza or bread dough in the refrigerator overnight or at room temperature until softened.

In a large skillet, cook the Italian sausage (casings removed) and chopped onion over medium heat for 10 minutes, breaking up the meat with a spoon.

Allow the sausage mixture to cool slightly.

Preheat oven to 375°F (190°C).

Lightly flour a surface and pat out one piece of dough into a 14x9 inch rectangle.

Sprinkle half of the cooled sausage mixture, grated mozzarella cheese, parmesan cheese, and chopped parsley evenly over the dough, leaving a 1-2 inch border along one long edge.

Roll the dough tightly from the long side, creating a jelly roll shape. Tuck the ends underneath the roll.

Transfer the roll, seam side down, to a lightly greased baking sheet.

Repeat the process with the remaining dough and filling.

In a small bowl, whisk together the egg and water.

Brush the tops of both loaves liberally with the egg mixture.

Sprinkle sesame seeds over the loaves, if desired.

Bake in the preheated oven for 20-30 minutes, or until the crust is golden brown.

Remove the loaves from the oven and let them cool slightly before slicing.

Cut each loaf into 1 1/2 inch slices and serve.