Preheat oven to 450 degrees F (230 degrees C). Line a baking sheet with aluminum foil.

Cut radishes into halves; cut any large radishes into quarters. Stir olive oil and thyme together in a bowl and toss radishes in mixture to coat. Spread radishes onto prepared baking sheet; sprinkle with salt.

Roast in the preheated oven until tender but firm in the centers, tossing every 5 minutes, 15 to 20 minutes. Drizzle with lemon juice.