Combine red wine, chicken stock, rosemary and garlic in a large sauce pan. Bring to a boil over high heat, then continue cooking until liquid has reduced to about ¾ – 1 cup, about 25 minutes. Strain sauce, then set aside.
About 30 minutes before cooking, remove lamb from refrigerator to come to room temperature. Place on a plate and pat dry with a paper towel. Preheat oven. Set aside kosher salt and black pepper, then use remaining salt and pepper to season lamb on all sides.
Heat oil in a large cast iron or heavy bottom skillet. When hot, place lamb meat side down and cook until browned on all sides. Place panko, goat cheese, rosemary, garlic, remaining kosher salt and black pepper in a small bowl. Use a spatula or spoon to combine ingredients until well incorporated.
Use a pastry brush or spoon to spread Dijon mustard evenly on meat. Use hands to press goat cheese-panko mixture firmly on top of rack of lamb. Return lamb to cast iron skillet. Surround lamb with red grapes and a few sprigs of fresh rosemary. Cook until lamb has reached an internal temperature of 120-125F (for medium rare).
Cover loosely with aluminum foil, then allow meat to rest 8-10 minutes. When ready, cut into single or double chops and serve with a sprinkle of flaky sea salt, roasted grapes, and red wine sauce.