Combine the mustard with all the other ingredients up to and including the pepper, coat the meat with the mixture, cover and marinate in the fridge for approx. 12 hrs., remove approx. 1 hr. before cooking.
Wipe off some of the marinade. Make incisions in the meat all the way along the upper and lower thirds, but do not cut all the way through. Fold back the meat, spread the pesto into the cuts, stuff with the cured ham and spinach, fold the meat back over and tie up.
Heat a wide casserole dish in a preheated oven at 220°C. Salt the meat, place the oil and meat in the casserole dish.
To roast in the oven, brown the meat for approx. 15 mins., turn. Reduce the temperature to 180°C, cook for a further 1 1/4 hrs. (core temperature: approx. 70 °C, baste the meat with the juices every now and then. Leave the meat to rest for approx. 10 mins. before carving.