Pre-heat your grill to medium hot. Rub the hanger steaks with a little salt, pepper, and peanut oil. Set them aside. Place the potatoes on a medium stainless-steel bowl with the olive oil, rosemary, mustard, and a little salt and pepper. Toss to combine well. Place them on the grill over indirect heat for around 30 minutes, turning once.
Grill the steaks over direct heat to your desired temperature and let them rest a couple minutes. Meanwhile, dress the greens and plate. Slice the steaks into ½-inch medallions and plate.
Spoon the sweet chile sauce over the steaks and serve with the potato wedges and crème fraîche for dipping.