Place the mint and 2 tablespoons of the pine nuts in a food processor with 2 tablespoons warm water and 1/3 cup (80ml) olive oil. Process until smooth, then place in a bowl and season with salt and pepper.
Toss prawns with 1 tablespoon oil. Season with salt and pepper. Heat a frypan over high heat, add prawns and fry for about 1 minute each side or until just cooked through.
Mix the remaining oil and lemon juice, and season with salt and pepper. Toss the dressing through the leaves, then pile onto plates. Toss together prawns, beans and mint oil, and serve on leaves. Garnish with remaining pine nuts.