If using leftover lamb, slice it thinly and let it come to room temperature.
Blanch the fresh peas in boiling water for 1 minute, then drain and rinse under cold water.
In a small bowl, whisk together the mustard, vinegar, olive oil, honey, salt, and black pepper to create the dressing.
In a large bowl, combine the lamb, blanched peas, radishes, and mint.
Drizzle with the dressing and toss gently to coat.
Serve immediately, garnished with extra mint if desired.