Preheat the oven to 475°F (245°C). If using a pizza stone, place it in the oven while it heats and preheat for at least 30 minutes for a crispier crust.
Prep toppings: wash and thinly slice the mushrooms, bell pepper, onion, and any optional veggies. Pat spinach dry and halve the cherry tomatoes.
On a lightly floured surface, stretch or roll the pizza dough into a 12-inch round. Transfer to a greased pizza pan, parchment paper, or a well-dusted peel/inverted baking sheet so it won’t stick.
Stir Italian seasoning (and red pepper flakes, if using) into the pizza sauce. Spread about 1/2 cup sauce over the dough, leaving a small border.
Sprinkle mozzarella evenly over the sauce, then sprinkle on the Parmesan.
Top with mushrooms, bell pepper, cherry tomatoes, spinach, and red onion (plus olives/zucchini/broccoli if using). Drizzle olive oil over the veggies and season lightly with salt and pepper.
Bake 12–15 minutes, until the crust is golden and the cheese is bubbling. If using a stone, carefully slide the pizza onto the stone to bake.
Cool for 2 minutes, then top with fresh basil. Slice and serve warm.