Heat 3 Tbsp. oil in a medium pot over medium. Cook chile and garlic, stirring often, until garlic is golden brown and crisp, 3–5 minutes. Transfer to a small bowl (with oil). Season with a pinch of salt; set aside.

Wipe out pot. Heat remaining 3 Tbsp. oil over medium. Add onion and celery stalks, season with salt, and cook, stirring occasionally, until softened but not browned, 5–7 minutes. Add stock, increase heat to medium-high, and bring to a boil. Reduce heat to medium-low, bring to a simmer, and add chickpeas. Continue to cook until chickpeas are warmed through and creamy but not mushy (this won’t take long since the chickpeas are already cooked), about 5 minutes. Season with salt.

Meanwhile, stir yogurt and a big pinch of salt in a small bowl. Mix cilantro and celery leaves in a medium bowl and squeeze lemon halves over. Season with salt and toss to coat.

Divide soup among bowls. Add a dollop of yogurt, then top with cilantro-celery salad and reserved garlic-chile oil.