Create a marinade by combining the oregano, bay leaves, garlic, cumin, water, orange juice, water, lime juice and salt in a blender or food processor. Blend until the herbs and garlic are finely chopped.
Pour the marinade over the pork butt and spread the mixture all over the outside of the roast on all sides. Refrigerate overnight, turning occasionally.
Roast at 135°C (275°F) on convection for 3½ hours.
Raise the oven temperature to 204°C (400°F) and cook for 10 minutes or until the pork is crispy on the outside.
Remove the pork from the oven and rest on the counter for about 20-30 minutes before carving.
Strain the pan drippings and skim the fat separately, reserve.
Add 3 Tbsp. of pork fat and onions to a large skillet and caramelize until brown on all sides.
Add reserved drippings to the onions and mix well.