On the stovetop, caramelize the onions, mushrooms, and bell peppers on medium-high heat. (See in-post notes about caramelizing vegetables).
Lay out the pizza crust dough on a piece of parchment paper or silicone baking mat. Cut the dough in half.
Assemble the Stromboli by spreading on about 2 tablespoons of the cheese sauce onto the pizza crust*(see note).
Then, add 6-8 slices of roast beef, the vegetables, and finally 3-4 provolone cheese slices.
Lightly spray the air fryer basket with avocado oil.
Roll the rectangles of dough up into logs, like you would with cinnamon rolls. Pinch the edges together and tuck and pinch the ends under. Brush the tops of the Stromboli with the egg wash. Sprinkle additional cheese over top if desired. Use a sharp knife to gently cut a diagonal slit, every 2 inches, on the top of each Stromboli.
Place one of the logs in the air fryer basket. Cook at 340°F/170°C for 8-10 min, or until the dough is cooked.
Sprinkle on shredded provolone cheese (optional) and cook for an additional 2-3 minutes, or until cheese is melted and crust is golden.
Carefully remove from the air fryer basket and cook the other log.
Enjoy as is or serve with the provolone cheese sauce.
Provolone Cheese Sauce
Melt butter in a medium saucepan over medium heat. Let the butter cook for 30 seconds or so to evaporate water. It should bubble up, but don’t let the butter brown.
Add flour and cook the flour, stirring continuously, for no more than 2 minutes, or until flour turns slightly golden. (This Is called white roux, which will thicken the cheese sauce and make it nice and smooth.)
Slowly pour in milk into the roux, while whisking the mixture continuously. Once all the milk is added, cook it for another 2-3 minutes, or until the mixture comes to a boil.
Remove from heat and stir in cheese. Whisk until the cheese is fully melted. Season with salt and pepper to taste.
Let it cool and thicken slightly before using.
Notes
*The provolone cheese sauce as the base is optional. I think it makes the Stromboli more cheesy, juicy, and delicious. You can omit it as a base on your dough and use it just as a dipping sauce. Or you can omit it altogether. Provolone cheese sauce recipe comes from Sweet & Savory.