Start by heating that olive oil in a large skillet over medium heat. Once it’s shimmering, toss in the thinly sliced steak. Sear it briefly until it's browned, about 2 to 3 minutes for a medium-rare result. Next, add in the onions, bell pepper, and mushrooms. Stir them around and let everything cook for another 3 to 4 minutes until the veggies are tender. Don’t forget the minced garlic; toss it in and cook for about 30 seconds until fragrant. Drizzle in the balsamic vinegar and season with salt and pepper.

Now, time to get the oven roaring. Preheat it to 400°F (200°C). This way, once we assemble the calzones, we can pop them right in for that gorgeous golden finish.

While the oven heats up, roll out your pizza dough on a floured surface. You want it about 1/4 inch thick. Using a round cutter or a large bowl, cut out circles (about 6-8 inches in diameter). You can typically get 4 to 6 circles per tube.

Here’s where it gets fun! Place a generous scoop of your cheesy steak mixture onto one half of each dough circle. Don’t be shy! Now sprinkle shredded provolone cheese generously over the top. Fold the other half over to create a pocket. Using your fingers or a fork, crimp the edges to seal them tightly. Transfer the calzones onto a baking sheet lined with parchment paper sprinkled with cornmeal for a crisp base.

Whisk the egg and water in a small bowl. Brush this egg wash over the calzones. This little trick gives them that beautiful golden color once they’re done baking. Sprinkle with Parmesan cheese and a dusting of red pepper flakes if you like a little heat. Slide those pockets of goodness into your preheated oven and let them bake for about 15-20 minutes, or until they’re deeply golden brown.

Once they’re out of the oven, let them sit for a few minutes. Then serve with marinara sauce for dipping and, if you want to add a touch of greenery, sprinkle some freshly chopped parsley on top!