1. Place oven rack on lowest shelf. If you have a stone, place it on rack. Preheat oven to 550°F, or your oven's highest temperature, for 45 minutes.
2. With motor running, drop garlic into feed tube of a food processor. Scrape down sides of bowl. Add chickpeas, tahini, lemon juice, salt, pepper and 2 Tbsp. water. Puree until smooth.
3. Dust a 14-inch-wide pizza peel with cornmeal, then flatten dough on top. Using lightly floured fingers or a floured rolling pin, stretch dough into a 13- to 14-inch round. (Sprinkle peel with more cornmeal if necessary to make sure crust slides around easily on peel.) Brush 1 1/2 Tbsp. oil over crust.
4. Spread hummus over crust, leaving a 1-inch border. Scatter peppers, feta, olives and crushed red pepper over pizza. Drizzle remaining 1 1/2 Tbsp. oil over pizza.
5. Carefully slide pizza onto stone. Bake until crust is golden brown on edges and on bottom (lift an edge to check) and cheese is lightly browned, about 8 minutes. Transfer to a cutting board. Sprinkle onion slices over pizza. Let rest for a minute; slice and serve.