Make the marinade and cool it to room temperature: add the jam, coconut aminos, tomato paste, almond butter, honey (if you’re not doing a Whole30), fish sauce, Chinese five spice powder, and ground ginger to a small saucepan. Whisk the marinade as you heat it to a simmer over medium heat.
Once the sauce is smooth and bubbling, transfer it to a measuring cup and cool to room temperature. (You can store the marinade in the fridge for up to 4 days and use it when you’re ready to roast the pork.)
Next, prepare the pork. Blot the pork shoulder dry with a paper towel and slice the meat into 2-inch strips of even thickness. The pork strips should be roughly uniform in size. (It’s cool to have fatty pieces of pork because you don’t want want to end up with dry char siu.)
Sprinkle the kosher salt all over the pork pieces. Place the pork in a large bowl or zippered storage bag and pour all except ⅓ cup of the cooled marinade onto the pork. Cover the reserved marinade and store in the fridge.
Use your hands to coat the marinade all over the pork strips. Cover the bowl with a silicone lid or plastic wrap and store in the fridge for 2 to 24 hours.
When you’re ready to roast the pork, preheat the oven to 350°F with the rack in the middle position. Place the pork on an oven-safe wire rack in a rimmed baking sheet.
Roast the pork for 30 minutes, flipping the pork pieces at the halfway point (15 minutes).
Remove the pork from the oven and increase the oven temperature to 400°F.
Brush half of the reserved marinade on the top of the pork pieces. Pour enough water into the bottom of the pan so that you have a thin layer coating the bottom. The water will keep the drippings from burning while the pork cooks.
Roast the pork for 25 minutes, and then flip the pieces over and brush on the remaining marinade. Roast for an additional 20 to 30 minutes or until the pork is slightly charred on the edges.
Rest the pork for 10 minutes, and then slice against the grain into chompable slices. Arrange the pork on a serving dish and garnish with sliced scallions, and serve! Leftovers can be kept in the fridge for up to 4 days or frozen for 4 months.