Heat a BBQ hotplate over medium-high heat. Place prawns in a bowl and drizzle with oil. Season with salt and pepper. Cook for 3 minutes on each side or until charred and cooked through. Transfer to a plate.

Place lettuce in a bowl. Using a spoon, scoop watermelon into bowl with lettuce. Add prawns, blueberries, mint and feta.

To make the dressing, whisk oil, lime juice and horseradish together in a jug. Drizzle over salad before serving.