Preheat oven to 450°F (232°C).
Roll out whole wheat dough on a parchment-lined baking sheet to desired thickness.
Spread tomato sauce evenly over the dough, leaving a 1-inch border for the crust.
Layer baby spinach, bell peppers, and red onions over the sauce.
Sprinkle mozzarella cheese and dried oregano uniformly over the vegetables.
Bake for 10 to 12 minutes until the crust is golden brown and cheese is fully melted.
Remove from oven and let rest for 2 minutes before slicing into 8 pieces.