Rib-Eye Steak with Grilled Potato Salad

Cover potatoes with water in a medium saucepan. Bring to a boil, reduce heat, and simmer until just barely tender, 10 minutes. Drain potatoes, cool, and cut in half. Whisk olive oil, vinegar, mustard, capers, garlic paste, salt, and pepper in a serving bowl until combined. Add frisée, radishes, and chives (but do not toss). Prepare a charcoal or gas grill with a hot fire. Place a cast-iron skillet on grill and close lid to heat skillet. Rub steak all over with dry rub and season with peppercorns and salt. Thread potatoes onto skewers; coat with olive oil cooking spray. Place potatoes, cut side down, on grill next to skillet and grill until light golden brown, 8 minutes, turning once. Remove potatoes from skewers, place in bowl with the greens and dressing, and gently toss to combine. Brush grill grates clean. Lightly spray both sides of steak with olive oil spray. Place steak into hot skillet on grill; sear steak for 11/2 minutes per side. Remove steak from skillet and place directly on grill grate. Grill, covered, 7 minutes for medium-rare doneness(135 degrees F) or 10 minutes for medium (145 degrees F), turning once. (The skillet sears the steak quickly so juices get sealed in; plus, the fat drips into the skillet instead of the grill, which means fewer flare-ups.) Remove steak from grill; let rest on a cutting board 5 minutes. Cut steak across the grain into thick slices. Serve with grilled potato salad.