Preheat oven to 400 degrees F. Move the rack to the middle position.
Cut the radishes into equal-sized pieces. If they're particularly large radishes, cut them into quarters. Otherwise, simply cut them into halves. The goal is to have pieces that are of equal volume.
Add the radishes to a mixing bowl with the olive oil, salt and pepper. Toss the radishes until they are fully coated and seasoned.
Place the radishes on a baking sheet and face down if you want them to brown nicely.
If the radishes are small, roast them for 15 minutes and check to see if they're done. If they're larger, it may take up to 30 minutes. Check on them every 10.
While the radishes are roasting, let’s make the pesto!
Add the garlic, radish greens, walnuts, sea salt, and olive oil to a food processor and puree until the ingredients are fully chopped and form a nice even sauce.
Once the radishes are done roasting, top with the pesto and enjoy!