To make the tomato sauce: Heat the olive oil in a medium pot or braiser over medium heat. Add the garlic and cook until fragrant, about minute, then stir in the tomatoes, salt, and oregano. Simmer until the mixture thickens slightly, about 10 minutes. Set aside and store any leftovers in the refrigerator for up to 5 days.
To make the pizza: Preheat an oven or grill (whichever you prefer for cooking pizza) and let the pizza dough rest, covered, at room temperature while preheating and prepping.
Stretch the dough into a 12-inch circle and place on a floured pizza peel. Spread the tomato sauce over the dough. Top with the olives and onion, then sprinkle with the mozzarella cheese. Bake until the cheese is bubbly and the crust is golden brown and cooked through. (The cook time will depend on your chosen pizza-making method.)
To serve: Sprinkle with Parmesan and crushed red pepper flakes, then serve warm.