Place a mandoline or carefully use a chef's knife to thinly slice the radishes and cucumbers into a mixing bowl, aiming for uniform, translucent rounds.
Add the chopped fresh mint leaves to the sliced vegetables, distributing evenly to ensure herbal freshness in every bite.
Pour the freshly squeezed lemon juice over the vegetables and mint, then drizzle with olive oil if using. Toss gently with salad tongs or two spoons until all ingredients are coated evenly and the slices are slightly wilted from the acid.
Season the salad with salt and black pepper to taste, tasting and adjusting until the flavors are balanced and bright.
Transfer the salad to a serving platter, arranging slices artfully to showcase their thinness and color. Serve immediately for maximum crunch and freshness.