Prep oven and baking sheet.
Heat oven to 350°F. Line a large baking sheet with parchment paper.

Rinse, drain and dry the chickpeas.
Rinse the chickpeas thoroughly in a colander until they are no longer foamy and the water runs clear. Drain thoroughly. Spread the chickpeas out on a clean towel and rub the chickpeas thoroughly with the towel to dry them off as much as possible, discarding any skins that happen to fall off while drying.

Season.
Transfer the chickpeas to a large mixing bowl. Drizzle evenly with the olive oil, then sprinkle on the sumac, smoked paprika, garlic powder, salt and pepper and toss gently until evenly coated.

Bake.
Spread the chickpeas out in an even layer on the prepared baking sheet. Bake for 45 minutes, pausing to shake the pan briefly at the 15- and 30-minute mark, or until the chickpeas feel dry and crispy to the touch.
NOTE: They will continue to crisp up even more as they cool after baking.

Serve.
Serve immediately, or store in a jar or bowl uncovered (or lightly covered with a thin kitchen towel or paper towel) at room temperature for up to 3 days.