Preheat the oven to 400 degrees . Place the chickpeas in a medium bowl and discard any loose skins. Toss with the olive oil, salt, black pepper, cumin and cayenne until evenly coated. Spread the chickpeas on a large rimmed baking sheet and bake, stirring occasionally, until golden and crisp, about 25 minutes. Remove from the oven and quickly stir in the thyme and pistachios, if using. Bake until crunchy, about 10 minutes more. Let cool and serve at room temperature.