Preheat oven to 450 F. (230 C.) Wash 3 bunches of rainbow carrots and slice off the stems. I like to leave about 2-3 inches of stem. It just looks prettier.
Place carrots on a foil-lined baking sheet. Drizzle with 2 tbsp. olive oil, and use your hands to make sure each carrot is nicely coated. Give carrots a good sprinkle of salt and pepper.
Roast for 20 minutes.