1. Bring a large saucepan filled with water to a boil over medium-high. Add radishes, asparagus, and snap peas; cook 3 minutes or until crisp-tender. Drain. Plunge radish mixture into a bowl filled with ice water; let stand 2 minutes. Drain.
2. Heat a small saucepan over medium. Add butter to pan; cook 2 minutes or until lightly browned and fragrant. Remove pan from heat; stir in rind, 1/4 teaspoon salt, and 1/4 teaspoon pepper.
3. Combine arugula, parsley, and mint in a large bowl. Add remaining 1/4 teaspoon salt, remaining 1/4 teaspoon pepper, oil, and 1 tablespoon juice; toss. Arrange arugula mixture on a platter; top with radish mixture. Drizzle with butter mixture and remaining 2 teaspoons juice. Serve immediately.