Preheat oven to 400 degrees. Cut trimmed radishes in half, toss with olive oil, salt, and pepper and place cut side down on a baking tray. Roast for 15 minutes. Once the radishes have cooled, put a spoonful of pesto on top and serve.
Blend all ingredients in a food processor, adding more olive oil if needed. Use with pasta, veggies, pizza, salad dressings, or whatever inspires you. You can replace some of the radish greens with basil or parsley to make a milder pesto.