Preheat oven to 350°. Toast pistachios on a rimmed baking sheet or sheet of aluminum foil, tossing occasionally until golden brown, 6-8 minutes. Let cool. Chop coarsely. Toasted pistachios can be made ahead and stored in refrigerator in a tightly sealed container.
Toast coriander seeds:
Toast coriander seeds in a small dry skillet over medium heat, tossing oftenm until fragrant, about 1 minute. Cool and chop coarsely, grind in spice mill or crush with a morter and pestle.
Whisk garlic, lemon juice, red pepper flakes and crushed coriander seed in large bowl. Whisk in oil. Season to tase with salt.
Combine carrots and dressing, toss and let sit at least 30 minutes. Carrots and dressing can be made up to one day ahead. Cover and chill. Toss carrots with cilantro and pistachios just before serving.