Place a rack in center of oven; preheat to 425°. On a large baking sheet, toss chickpeas, 2 tablespoons oil, juice of ½ lime, and 1 teaspoon salt. Spread in an even layer.

Roast chickpeas, stirring halfway through, until crispy, about 30 minutes. Add chili powder, toss to coat, and continue to roast until color slightly deepens, about 5 minutes more. Transfer to a plate and let cool.

On same baking sheet, toss corn with 1 tablespoon oil. Roast until just starting to take on color, 8 to 10 minutes.

Meanwhile, in a small bowl, toss onion, tomatoes, 1 tablespoon lime juice, and a pinch of salt. Let sit until ready to use.

In a blender, blend yogurt, garlic powder, onion powder (if using), half of jalapeño, cilantro stems, half of cilantro leaves, one-quarter of avocado, 2 tablespoons oil, juice of 1 lime, and ½ teaspoon salt until smooth. Taste and adjust seasonings as needed.

On a platter, combine tomato mixture, corn, remaining jalapeño, and half of remaining cilantro leaves; season with salt, if needed. Spread in an even layer. Top with chickpeas, remaining avocado, and a drizzle of dressing. Sprinkle with feta (if using), chives, and remaining cilantro leaves.