Preheat the oven to 425F and have one rack set in the centre. You will also need one in the upper part of the oven for broiling the pork at the end. Line one or two rimmed baking sheets with foil for easy clean up, and set aside.
Transfer the marinated pork to the prepared baking sheet, scooping away any excess marinade. Add the diced pineapple to the baking sheets, using the excess marinade on the pork to coat the pineapple. If needed, you can use some of the excess sauce that is in the bag. Make sure everything is in one layer.
Transfer the pork to a cutting board & carefully chop it into bite-sized pieces. Drain all excess liquid from the baking sheets carefully, keeping the pineapple on the sheets. Return the cubed pork back to the baking sheet keeping everything in one layer.
Place the baking sheet under the broiler. Broil 6-8 minutes, turning the pork and pineapple over half way through, until the al pastor pork is browned and crisp. Make sure that the rack is set close to the broiler or else it may take a while which will only dry out the meat. Keep an eye on it to prevent scorching.
Sumac Pickled Onions, adapted from Jeanine's recipe from over at Love and Lemons:
1 small red onion
1 cup white vinegar
1 cup water
3 tbsp sugar
1 tbsp salt
1 tsp sumac
Thinly slice the onions (a sharp knife, but a mandoline is your friend) Place in a medium mason jar with a lid.
Heat the vinegar, water, sugar and salt in a saucepan set over medium heat. Stir till the sugar is completely melted. Let it cool down and then pour it over the onions. Stir through the sumac and let it cool down, and then seal and store in the fridge for up to two weeks.
See blog post for the recipe for the Cilantro Lime Rice, and link to my classic Poblano Pepper Guacamole.