In a kettle of boiling salted water cook sugar snap peas 2 minutes. Add snow and green peas and cook 1 minute. Drain peas in a colander and rinse in cold water. Pat dry on paper towels. In a small bowl whisk together lemon juice, sugar, salt and oil until sugar is dissolved. In a larger bowl toss all peas with dressing and radishes. Line a serving platter with pea greens, and spoon salad onto plate. Sprinkle with chopped mint.