Preheat oven to 400 degrees F. Add olive oil to a large Ziploc bag. Add carrots to the bag, seal and shake until all carrots are coated with oil. Sprinkle ranch dressing mix in the bag, seal and shake until carrots are evenly coated. Spray a baking sheet with nonstick cooking spray. Spread carrots on baking sheet in a single layer. Cook for 30 minutes (or until carrots are soft), stirring halfway through.