Roast: Preheat oven to 400 degrees F (204 C). Dice beets and radishes, and spread onto a parchment paper lined baking sheet. Drizzle with oil and season with salt and pepper, tossing around a bit to evenly coat. Roast for 20 minutes, or until radishes are a bit tender (beets will still have some crunch)
Serve: Toss to combine roasted beets, radishes, feta, pesto, and the juice from half of a lemon. Serve warm or cold.