Season the racks of lamb with salt and pepper. Heat a grill pan or barbecue to medium-high and brush with oil. Sear the lamb for 2 minutes on each side to brown. Place racks on a plate and allow to rest until cool enough to handle.
Preheat oven to 400° F. Combine all filling ingredients and mix well. Cut racks into individual chops. Using a small, sharp knife, cut a slit widthwise into each chop to about 1/2 inch from bone. Butterfly open and place a spoonful of the filling on one side, then fold over the other side to enclose.
Place chops on a lined baking sheet and bake for 5 minutes or until cooked as desired. Cheese will be melting.(They can also be cooked on the grill for 1-2 minutes each side.)
Meanwhile, heat 1 tablespoon of oil in a large pan over medium heat and cook shallot until golden brown. Add the spring onions, mushrooms and water or wine, and cook until mushrooms are just tender. Add the spinach, cover, and cook just until wilted. Stir, season to taste and keep warm.
Serve the chops over the spinach and mushrooms with lemon wedges and bread on the side.