Heat the oil in a large skillet over medium-high heat. When hot, cook the chorizo for 3 to 4 minutes. Once the chorizo starts rendering its fat and browning a bit, add the bacon and cook for 2 to 3 minutes, until it begins to brown. Add the onion, celery, apple and plantain, and cook until softened and cooked through, about 6 to 7 minutes. Add the almonds and salt, stir and remove from heat.
Scrape the filling onto the butterflied loin - if you have two pieces, divide it among both pieces. Spread all over, leaving about an inch around the edge so the filling doesn’t escape as you roll up the loin. Gently roll up the loin, without trying to pack or squeeze as you do - just try to contain the filling within the loin.
Place the rolled loin on a chopping board, and using butcher’s twine, roast tie the loin at intervals of about 1” from top to bottom. Return it to the the baking dish with the marinade, cover with aluminum foil and roast for 50 minutes. Raise heat to 400, remove the baking dish from oven, carefully take off the foil, and place back in the oven uncovered. Roast for another 25 to 30 minutes, until the meat has reached an internal temperature of at least 145 degrees and the top has beautifully browned. Remove from the oven, cover loosely with aluminum foil, and let it sit for at least 10 minutes before cutting off the twine and slicing.
To serve, slice and place on a platter, then pour the remaining marinade from the baking dish on top.