Soak the farro in warm water for about 20 minutes. Drain and rinse well. Pour into a medium saucepan with enough water to cover by 1 inch. Cover the pot and bring to a boil, and then reduce to a simmer. Add a pinch of salt and cook for about 30 minutes. The farro should be soft but have a slight chew to it. Drain to remove excess water, and then transfer to a bowl and toss with 2 tablespoons of the olive oil. Set aside.
Preheat the broiler.
Toss the shrimp with 2 more tablespoons olive oil, some salt, pepper and the lime juice. Spread in an even layer on a baking sheet and broil for 10 minutes, flipping halfway through. Let cool slightly.
Make the salad dressing by combining the remaining 1/4 cup olive oil, the mint, lemon juice and some salt and pepper in a small jar. Cover and shake to combine.
Toss together the farro, beans and watercress in a large bowl with half of the dressing. Season with salt and pepper. To plate, transfer the salad to a large platter and top with the shrimp. Serve with the remaining dressing on the side.
Recipe courtesy of Gabriele Corcos and Debi Mazar