Heat 1/4 cup oil in a saucepan over medium heat. Add onion, and cook until softened, about 8 minutes. Add garlic, and cook, stirring, 2 minutes. Add chickpeas, and cook 3 minutes. Remove from heat; let cool 15 minutes.
Add chickpea mixture, mint, parsley, lemon juice, and salt to a food processor, season with pepper, and puree. With machine running, add remaining 1/4 cup oil in a slow, steady stream, mixing until emulsified. Transfer to a serving bowl, and drizzle with oil. Serve with pitas.