Butterfly the pork belly. Pat the pork belly dry with paper towels, and lay the belly out flat with the fat side down. Use a sharp knife to make two main cuts, starting from the middle and following the natural rib line outward so that the pork belly opens like a tri-fold project board. Stop about 1 inch from the edge so that you don’t cut all the way through the belly, and so that you don’t accidentally tear the meat as you’re opening it up. As you gently unfold the pork belly, make small cuts as needed to even out the thickness.
Make the seasoning mixture. Add minced garlic, finely chopped rosemary and thyme, and the zest of 2 lemons to a small bowl. Mix together well.
Preheat the grill. Heat pellet grill or smoker to 375℉ with your choice of wood or pellets.
Season the pork belly. Season the open pork belly with a liberal amount of salt and black pepper. Then evenly sprinkle on about ⅔ of the herb, garlic, and lemon zest mixture. Close the two side “flaps” and season the tops of those with salt and pepper and the remaining herb mixture.
Roll the seasoned pork belly. Tightly roll the pork belly into a log shape with the skin on the outside. Use butcher twine to secure the roll every 1-2 inches so that the porchetta holds its shape as it cooks. *TIP - It's easier to have two people for the rolling and tying process - one person holds the pork belly in the rolled shape while the other ties the knots with the twine.
Oil and season the outside. After tied, rub about 2 tablespoons of olive oil all around the pork belly log. Sprinkle evenly with about 1 tablespoon of salt.
Cook the porchetta on the grill or smoker. Place the rolled pork belly on a wire rack, and transfer to the grill grates. Cook at 375℉ until the internal temperature of the pork belly reaches about 175℉. *This took about 2½ hours at 375℉, but cooking times may vary.
Crisp up the skin. Adjust the grill temperature up to 400℉. Cook the pork belly an additional 20-30 minutes, until the internal temperature is about 185-190℉ as read by an internal meat thermometer. *Optional - You can also use a mini propane torch to crisp up the skin even more.
Rest and slice the porchetta. Remove the porchetta from the grill and allow to rest until the internal temperature comes down to about 150℉, about 30 minutes. Cut into thin slices if serving on a sandwich or thicker slices for plating as a main dish. *For a sandwich, serve plain on soft warmed baguette. Squeeze a bit of lemon juice on top of the sliced porchetta if you wish.