Heat oven to 425° F. On a large rimmed baking sheet, toss the potatoes, 2 tablespoons oil, and ¼ teaspoon each salt and pepper. Roast until golden, 25 to 30 minutes.
Meanwhile, in a food processor, finely chop the parsley, pistachios, and garlic with ¼ cup oil and ¼ teaspoon each salt and pepper.
Heat the remaining tablespoon of oil in a large skillet over medium-high heat. Season the steaks with ½ teaspoon each salt and pepper.
Cook the steaks to the desired doneness, 4 to 6 minutes per side for medium-rare. Transfer to a cutting board.
Wipe out the skillet. Add the broccoli rabe and ½ cup water and simmer, covered, until tender, 2 to 3 minutes.
Slice the steak and serve with the broccoli rabe, potatoes, and pesto.