Drain the canned tuna and place it in a large mixing bowl, breaking it apart gently with a fork.
Trim and thinly slice the radishes on a cutting board, revealing their peppery, crisp interior.
Add the sliced radishes to the bowl with the tuna and give everything a gentle stir to combine the flavors.
Wash and dry the mixed greens, then layer them onto a serving plate or bowl as the base of the salad.
Squeeze fresh lemon juice over the tuna and radishes, then drizzle with olive oil, creating a fresh, citrusy dressing.
Season with salt and pepper to taste, then gently toss the salad to coat everything evenly with the dressing.
Arrange the seasoned tuna and radish mixture on top of the greens, creating a colorful and textured presentation.
Serve immediately and enjoy the crisp, bright flavors with each bite.