Make homemade pizza crust and let it rise. If you haven't made Garlicky Tomato Sauce, do it now.
Adjust oven rack to lowest position and heat oven to 550 degrees. Season spinach with oil, garlic, salt and pepper and toss to coat; set aside. Season red onion with a touch of oil and a light sprinkling of salt; set aside.
When oven reaches temperature, bake pizza crust until golden brown, about 10 minutes. When crust emerges from the oven, spread with Garlicky Tomato Sauce, top with spinach, olives, red onion, and feta.
Reduce oven temperature to 500 degrees and bake until topping are heated through and crust is crisp and brown, about 10 minutes. Slide pizza onto a cutting board, garnish with oregano, cut into squares, and serve.