Step 1Heat the oven to 325 degrees. In a large skillet over medium-high heat, heat the oil. Season the pork with 1 1/2 teaspoons salt and one-fourth teaspoon pepper, place it in the skillet and sear, turning occasionally, until deep golden brown all over, about 15 minutes total.
Step 2Meanwhile, put the broth, juice, vinegar, zest, adobo sauce, cumin, garlic, chiles, onions, one-half teaspoon salt and one-fourth teaspoon pepper into a blender; puree until smooth.
Step 3Transfer the pork to a large, deep casserole dish and set aside. Pour the excess fat out of the skillet. Carefully pour about 1 cup of the chipotle-orange puree into the skillet and cook briefly, scraping up any browned bits. Pour the contents of the skillet over the pork along with remaining chipotle-orange puree. Scatter the bay leaves and thyme in the casserole; cover tightly with foil. Top with a tight- fitting lid; bake for 2 1/2 hours.
Step 4Carefully uncover the pork and flip over the roast. Baste it with the juices, then re-cover with the foil and lid and return to the oven. Continue cooking until very tender, about 2 hours more. Set aside, covered, for about 30 minutes, then uncover and pour the contents of the casserole into a colander set over a large bowl; discard bay leaves and thyme.
Step 5When cool enough to handle, tear the pork into shreds, discarding any fat, and transfer to a large bowl. Skim off and discard fat from the juices, then add the juices to the shredded meat and toss well. Pile the pork onto brioche rolls and top with grated cheese, if desired.