Preheat oven to 425°F. Rub lamb with oil and salt. Place in a roasting pan, fat side down. Roast 8 minutes. Turn and continue roasting 8 minutes. Remove from oven, leaving oven on.
Combine mustard, bread crumbs, garlic, pecans, 2 tablespoons rosemary, and goat cheese. Spread over lamb. Return to oven and cook 15 minutes, until crust is golden brown. Remove from oven and cover with foil to keep warm.
In saucepan, combine balsamic vinegar and remaining 2 tablespoons rosemary and let simmer for 6 to 8 minutes or until reduced to half.
Slice lamb into individual chops and drizzle sauce over chops. Serve with roasted butternut squash.