Preparation

Make the roast lechon

• In the bowl of a food processor, pulse the cilantro, parsley, scallions, garlic, cumin, and lime and orange juices until combined but not completely smooth. The mixture should have a chunky texture. Put the pork in a 2-gal. zip-top bag, and add the marinade. Seal the bag, and toss and massage the pork to coat all over with the marinade. Marinate overnight in the refrigerator.
• Position a rack in the center of the oven, and heat the oven to 275°F. Remove the pork from the refrigerator about 1 hour before cooking to bring it to room temperature. Remove the pork from the marinade, discard the marinade, and season the pork well with salt and pepper. Place fat side up in a large baking dish or Dutch oven, cover with foil or a lid, and bake for about 40 minutes per lb., until the pork reaches an internal temperature of 180°F when tested with an instant-read thermometer, 2-1/2 to 3 hours.
• Remove the pork from the oven. When cool enough to handle, shred the meat, discarding any skin or fat. Strain the cooking liquid, skim off and discard any fat, and mix a little of the cooking liquid with the pork, reserving the rest for reheating the pork if you are not making the sandwiches right away. Season with 1 tsp. salt and 1/2 tsp. pepper. The pork can be made up to 3 days in advance. Store well-wrapped in the refrigerator.

Make the pickled jalapeños

• Combine the vinegar, 2 cups of water, sugar, salt, and peppercorns in a medium saucepan. Warm over medium-low heat to dissolve the sugar and salt. Add the carrots to the hot liquid. Let sit 5 minutes. Meanwhile, put the jalapeños in a bowl that has been placed over a bowl with an ice bath. Pour the carrot mixture over the jalapeños. When cold, pour into an airtight container, and store in the refrigerator for up to 2 weeks.

Make the mustard spread

• In a medium bowl, stir together the mayonnaise, Dijon, and yellow mustard.

Make the sandwiches

• If the pork was made ahead and refrigerated, warm it slightly in a medium Dutch oven with about 1/2 cup of the cooking liquid. Split the loaves of bread lengthwise, keeping them attached on one side so that they open like a book. Spread 2 Tbs. of the mustard spread on each side. On one side of the bread, layer the sliced chorizo slightly overlapping to completely cover the bread. Top with the pork, then top with the cheese, pickles, and jalapeños to taste. Close the sandwich.
• Cut each sandwich into 3 equal portions. Spread about 1 tsp. of butter over the tops of each sandwich, and wrap each separately in aluminum foil. Heat a griddle or large skillet over low heat. Put the sandwiches on the griddle, and heat on both sides for 5 to 6 minutes (press the sandwiches with either another pan or a small cookie sheet on each side to flatten a little). Carefully remove the foil and serve.