Add the ham bone, water, apple cider vinegar, bay leaves and serrano pepper to the slow cooker. Set on high for 5 hours.
Remove the bone from the pot and take the meat off of it. Add the meat and bone back to the pot and cook for another 2 hours on high.
Next, add oil to a saute pan over medium heat, then add the onion, leeks and garlic cloves. Saute for 7-8 minutes, or until the onions have started to caramelize.
Add this to the slow cooker along with the remaining ingredients.
Cook for 3 hours on high, or until the vegetables are tender.