Season the chicken breasts with salt, pepper, and Italian seasoning. Cook them in a pan over medium heat until fully cooked (about 5-7 minutes each side). Set aside to cool and then chop into small pieces.

Preheat your oven to 400°F (200°C) to ensure even baking.

On a floured surface, roll out your pizza dough into a large rectangle.

Evenly spread a layer of Dijon mustard across the rolled-out dough for an extra kick of flavor.

Place the chopped chicken in the center of the dough, followed by the mozzarella cheese, Swiss cheese, and chopped spinach (if using).

Carefully roll the dough from one end to the other, tucking in the edges to create a sealed log.

Beat the egg and brush it over the top of the rolled stromboli. This will give it a beautiful golden color.

Place the stromboli on a baking sheet and bake for about 20-25 minutes, or until golden brown.

Allow to cool for a few minutes before slicing. Serve with marinara sauce for dipping.