Preheat the oven to 450°F and lightly grease a pizza pan.
Place the pizza dough ball on a lightly floured surface and roll it out into a thin circle. Transfer to the pizza pan. You can prick the dough all over with a fork or dough docker to avoid bubbles while baking.
Pre-bake the crust for 5-6 minutes in the preheated oven, until it just becomes firm (to avoid a soggy crust later).
Spread the marinara sauce on the pizza dough circle, leaving the edges (crust) bare.
Sprinkle the cheese on top of the sauce. Then arrange the spinach, kimchi, mushrooms and red onions evenly on top.
Return the pizza to the preheated oven and bake until the crust is golden and the cheese is fully melted, about 7 to 10 minutes.
Let cool for 2 minutes before slicing. Sprinkle with crushed red pepper flakes (if using) and serve!
Notes
These toppings have been measured out for a medium 12” pizza crust. You may need to adjust the topping amounts depending on the size of your pizza and personal preferences.