Soak garbanzo beans in a bowl full of water overnight or at least 8 hours.
Add the pork roast, beef, chicken thighs, and salt pork to a large pot over medium-high heat. Cover all the meat with water so that everything is just submerged. Bring everything to a boil.
During the first few minutes of boiling, using a spoon, skim off as much foam on the surface as you can. This will help with the clarity and color of your broth.
After 5 or 10 minutes of boiling and skimming, add 1 pound of garbanzo beans and 2 tablespoons of salt. Reduce the heat under the pot to a little bit above medium and place a lid on the pot but leave the lid slightly ajar so that some steam can be released.
Allow the meat and liquid to boil for 1.5 hours with the lid slightly cracked.
After 1.5 hours remove the pot lid and check the level of the water. If it is below the top of the meat, you can add a cup or two of water to make sure that everything stays submerged. If you add water, allow the liquid to start boiling again, and then add the blood sausage and fresh chorizo.
Boil for another 30 minutes with the lid slightly cracked open.
At this point, 2 hours should have elapsed, and the meat should be very tender. Take the pot off the heat and turn off the burner. Remove all the meat to 1 bowl to cool and remove the garbanzo beans to a second bowl. The garbanzo beans can be used with the broth later to create a soup. They will not be used in the making of the sandwich, but they can also be served on their own as a delicious side dish.
The bowl full of meat is the pringá and it will be used in the sandwich. You can save some of the meat to put back in the broth for soup if desired.
Once the meat has cooled enough that you can manipulate it with your hands, start removing the meat from the bones and cartilage. Be fairly thorough making sure you do not miss any small bones.
When the meat has been fully deboned, shred the chicken, beef, and pork roast into small pieces. Chop up the salt pork, remove the casings from the sausages, and chop the sausage meat if it's not falling apart already. Run your knife through all the meat to get it into small pieces.
Sandwich assembly: in a medium-sized skillet over medium heat add around 3/4 to 1 cup of meat mixture and cook it until the meat gets hot and starts to crisp up. Remove the meat to a small plate and wipe out the pan to use in the next step.
Slice your roll and add a teaspoon or so of olive oil to the bottom of the roll. Top the olive oil with a big pile of warm pringá meat.
Add slices of cheese if using and then close the top on the sandwich.
Add a teaspoon of olive oil to the still-hot pan and add the completed sandwich on top of the oil. Cook for 2 to 3 minutes and then flip the sandwich over, toasting the top of the roll for another 2 to 3 minutes or until the roll has browned and crisped up.
Serve the pringá while the roll and meat are hot.
Once you have fully boiled the meat you will have three things: the broth, cooked garbanzo beans, and a lot of meat.
Broth: You use the broth or cocido to create a soup. This is a very loose instruction on how to make a soup from the cocido. When it's 20 or 30 minutes before you want soup, put 1.5 to 2 cups per person you are serving in a pot on the stove. Bring the broth to a boil and then you can add vegetables like bite-sized pieces of potato or carrot. Boil these in with the broth for 15 to 20 minutes. Check the potatoes for tenderness with a knife to make sure they are soft. Once they are soft the soup is almost ready. Add about a 1/4 cup of cooked garbanzo beans per person and a small handful of meat per person. Cook for another 4 or 5 minutes until everything is warmed through and serve.
Garbanzo beans: the traditional use is in the soup described above. But you can serve these beans as a side dish, or you can place them on a sheet pan in a 425 F oven for 20 to 30 minutes until they become golden brown and crispy to serve as a snack.
Meat: You can reserve some of the meat (before chopping it all together), cut it into bite-sized pieces, and reserve it for garnish in the soup. You can also freeze this meat in zip-top freezer bags for up to 3 months. Just allow it to thaw and warm the meat up in a skillet for another future sandwich.