Toast coriander, cumin, cardamom and fennel in a hot pan on the stove. Cool seeds slightly and crush with your mortar and pestle. Add salt and brown surgar and dissolve in balsamic vinegar, then stir in olive oil. Place pork and cubed sweet potato and apple into a plastic lidded containerg and pour marinade overtop. Burp out air and seal. Marinade 2 - 4 hours turning container over periodically in the refrigerator.
Preheat oven to 350 degrees F (175 degrees C).
Place apple and sweet potatoes around pork loin (touching the meat) in a glass dish, along with marinade. Brush marindae on to loin and cook for 1 hour or until loin reaches 140 degrees F.