Preheat oven to 375°. Place lamb in a shallow roasting pan. In small bowl, combine the lemon zest, oregano, garlic, oil, salt and pepper. Rub over lamb.
Bake 30-40 minutes or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°). Let stand 5 minutes before cutting. If desired, serve with fresh oregano and lemon slices.