How to Make It
Preheat the oven to 350°. Light a grill. In a small bowl, combine 2 tablespoons of the olive oil with the lemon juice, fish sauce and a generous pinch each of salt and pepper. Set the dressing aside.
In a medium roasting pan, toss the potatoes with 2 tablespoons of the olive oil and season with salt. Roast for about 30 minutes, or until tender.
Meanwhile, in a small bowl, combine the garlic and herbes de Provence with the remaining 1/4 cup plus 2 tablespoons of olive oil and a generous pinch each of salt and pepper. Rub the mixture all over the steaks. Grill over high heat until browned but still medium rare, 3 to 4 minutes.
In a large bowl, toss the watercress with the dressing and Parmesan shavings and season with salt and pepper. Serve the salad with the steaks and potatoes and pass the lemon wedges at the table.