In a small bowl, combine the garlic powder, onion powder, salt, pepper, and oregano. Rub the mixture over all sides of the meat, pressing it to adhere (if the meat is tied together with twine or netting, just rub the seasoning right over it).
Prepare a grill to medium indirect heat. For a charcoal grill, scatter about half of the wood chips, if using, over the coals. For a gas grill, place about half of the wood chips, if using, in the grill’s smoker box. Place the pan with the pork on the grill over indirect heat, cover, and cook, adding more coals or adjusting the gas as necessary to maintain a temperature between 250 and 300 degrees F and adding more wood chips every 1 1/2 to 2 hours, until the pork is very tender, 5 to 6 hours.
Transfer the meat to a cutting board and let rest 10 to 15 minutes. Use two forks to shred meat into bite-sized pieces. Moisten/season with cooking juices and/or barbecue sauce to taste.
NOTE: The optional barbecue sauce is included because it’s traditional to mix grilled pulled pork with some sauce, but also because, especially with the sirloin roast, there aren’t really any pan juices to moisten the meat with. The meat doesn’t have to be moistened, but it’s a little better with a little juice – again, especially the sirloin.
Serving Suggestions: If you like, substitute another herb, like oregano or marjoram, for the thyme – or switch it to paprika. Try the pulled pork in a breakfast hash, as an enchilada filling, or in a submarine-type sandwich.
Nutrition per serving: Calories: 310; Fat: 20g; Saturated Fat: 7g; Cholesterol: 95mg; Sodium: 470mg; Carbohydrate: 1g; Protein: 30g; Fiber: 0g.