Combine onion, 2 tablespoons cumin powder and 2 tablespoons chili flakes in a large bowl. Add soy sauce and Shaoxing wine. Mix well until the onion is evenly coated with spices.

Place lamb on a large working surface, meat side up. Grind a generous amount of sea salt over the top side of the lamb and rub to season.

Spread plastic wrap on a working surface without cutting it, a bit larger than the size of the lamb breast. Spread half of the onion, garlic and ginger evenly over the plastic wrap and place lamb on top of onion, meat side down.

Grind sea salt over the bone side of the lamb and pat several times to let salt absorb well. Spread the rest of the onion, ginger, and garlic evenly over the lamb, taking care to not leave any inch of the lamb uncovered.

Wrap lamb in several layers of plastic wrap, until every inch of the lamb is covered well. Place in a large plastic bag and seal with a clip (or in a large tray sealed with plastic wrap). Marinate in fridge for 24 hours.

Transfer the lamb from fridge to kitchen counter and let it return to room temperature before roasting, at least for 1 hour.

Preheat oven to 190 degrees C (370 F).

Spread aluminum foil over a baking tray, shiny side up (*see footnote). Unwrap lamb and discard the plastic wrap (be careful not to leave any piece of plastic wrap on the lamb). Transfer the lamb, and all the onion, garlic and ginger to the foil. Wrap the lamb in several layers of foil until the lamb is fully covered, shiny side facing inward. Bake at 190 degrees C (370 F) for 50 minutes.

Transfer lamb to kitchen counter and allow it to cool down a bit until you can handle the foil.

Increase the oven temperature to 220 degrees C (430 F).

Mix the remaining 2 tablespoons cumin powder and chili flakes in a small bowl.

Unwrap foil carefully with tongs. Remove the onion and discard it. Sprinkle half of the cumin and chili mixture evenly over the lamb.

Carefully flip the lamp and place it on a roasting rack, and spread the remaining cumin and chili mixture on the other side.

Bake on the middle rack at 220 degrees C (430 F) for 20 minutes, until the lamb is cooked through and the surface is nicely charred.

Transfer lamb to kitchen counter and allow to cool until you can handle the lamb, about 15 minutes. Split the ribs and slice meat into thin slices.

Serve warm as a main over rice or mashed potato.