Mojo roast pork: place pork in a container with a lid or a zip-top bag that will hold it. 

Combine all other ingredients in a bowl and stir to integrate, creating the mojo marinade. Add 2/3rds of the marinade into the container/bag with the pork and massage to spread it all around. 

Refrigerate for 4 hours or overnight for best results. 

Preheat oven to 275 degrees. 

Remove pork from the container with the marinade and wrap it loosely with a double layer of aluminum foil. It's important to keep the foil loose at this point to let air circulate inside the foil package around the meat. 

Bake on a baking sheet for 2 hours. 

Open the top of the foil, exposing the top of the pork, and raise the oven temperature to 325 F and bake for another 2 hours. If you want, during these last 2 hours, you can pull the pork out and baste it with the accumulated juices in the pan/foil. 

Once the 2 hours are up, remove the pork from the oven and allow it to rest for 15 minutes. And then, using two forks or your hands, shred the pork into smaller bite-sized pieces. Add the pieces to a container with some of the liquid left in the bottom of the aluminum foil/pan, then pour over the last 1/3 of the marinade and mix the pork in with the marinade and accumulated liquid to combine it all. Store the meat and juices in the fridge in a sealed container for up to a few days. Warming the meat briefly in a pan on the stove or in the microwave before using it in a sandwich.

Caramelized onions: add 2 tablespoons of butter to a large pan over medium heat. 

When the butter is bubbly and frothing, add all of your sliced onions. Add a pinch of salt and stir everything to combine. 

Reduce the heat to medium-low and cook the onions, stirring often, for 20 minutes. 

After 20 minutes, your onions should be starting to become lightly tan-colored, but not browned. You might start to see dark brown spots forming on the bottom of the pan, though, and if you do see that, add a tablespoon or two of water to the pan with the onions and use that water to stir the dark parts at the bottom to keep things from burning. 

Continue cooking the onions over medium-low heat for another 15 to 25 minutes. Remember: if you see dark spots or dry areas on the pan, add a tablespoon or two of water. The water should cook off quickly, but it will help to temper the pan temperature and help the onions cook through without burning. 

After the onions are nice and turning brown, remove from the pan to a sealed container, and if not serving immediately, store in the fridge for no more than a week or so. 

Sandwich assembly: slice a baguette about 7 to 8 inches long and split it in half lengthwise. Toast it lightly.

Spread some garlic mayonnaise on both sides of the bread. Top the bottom slice with pickled jalapeno slices and cilantro.

Warm the pork and a pile of onions either in a pan, in the oven, or in the microwave (as mentioned above). Add as much pork as you'd like on top of the jalapeno slices and cilantro. Then layer the onions on top of the pork.

Add Romaine lettuce and close the sandwich to complete. Serve and enjoy.