Preheat the oven to 400°F (200°C) and line a rimmed baking sheet with a layer of paper towels.
Drain and rinse the chickpeas, then spread them on the paper towels and blot with additional towels until mostly dry.
Transfer the dried chickpeas to a medium bowl. Drizzle with 1/2 teaspoon olive oil and toss gently with a large spoon to coat evenly.
Add the chopped rosemary and 1/4 to 1/2 teaspoon sea salt, then toss again to distribute the seasoning.
Spread the chickpeas in a single layer on the prepared baking sheet.
Bake for 30 to 40 minutes, stirring once halfway through, until the chickpeas are golden brown and crunchy.
Remove from the oven, taste, and add additional sea salt if desired, then serve.