Place the olive oil and butter in a large pot on med high heat when sizzling add onion and cook for 2-3 min, stir in the spring onion and stir until cooked about 1 min, Add the garlic and preserved lemons along with the spinach cook until combined for about 2 minutes. Season to taste
Remove from the stove, add the Olives, herbs and cheese and stir to combine
Place the chicken on a clean work surface and lay it out flat. Season the open cavity with salt and pepper. Add the filling and spread out evenly, pushing into the legs and wings.
close the chicken back up to resemble a whole chicken. Truss the chicken to ensure it stays together during cooking. Season and rub with olive oil.
Add olive oil to base of heavy cast iron pot, heat on high and brown chicken on all sides to ensure it seals in the juices. Start with the bone-in sides first as these take longer to cook.
Place in covered casserole dish along with a few slices of thick cut lemon, in oven for 45-50min or until juices from thigh run clear. rest uncovered for 15min before carving to let the juices settle in the chicken.