Preheat your oven to 450°F (232°C) and place a cast iron pizza pan inside to heat up.
In a skillet over medium heat, cook the sausage, breaking it apart with a spatula, until browned and crumbled, about 8-10 minutes. Remove from heat and set aside.
Roll out the pizza dough on a sheet of parchment paper to fit the size of your pizza pan.
In a small bowl, mix together the olive oil, minced garlic, and Italian seasoning.
Once the pizza pan is preheated, carefully remove it from the oven and place the parchment paper with the pizza dough on top.
Spread the olive oil mixture evenly over the pizza dough.
Sprinkle the shredded mozzarella cheese and grated Parmesan cheese over the olive oil mixture.
Layer the cooked sausage, then the sliced mushrooms, and finally the spinach on top of the cheeses.
Return the pizza to the preheated oven and bake for 8 minutes.
After 8 minutes, carefully remove the parchment paper to allow the crust to crisp up directly on the preheated cast iron pan. (You can so this easily by using a spatula to elevate the pizza slightly from the parchment paper, ensuring no contact, and then slide it away.)
Continue to bake for an additional 12-15 minutes, or until the crust is golden brown and the cheese is melted and bubbly.
Optional: Sprinkle with red pepper flakes for a spicy kick.
Carefully remove the pizza from the oven and transfer it to a cutting board. Slice into wedges and serve hot.