Recipe courtesy Emeril Lagasse, adapted from Essential Emeril: Favorite Recipes and Hard-Won Wisdom from My Life in the Kitchen, Oxmoor House, 2015, courtesy Martha Stewart Living Omnimedia, Inc.
In a blender, combine the Asian pear, apple, onion, garlic, green onions, soy sauce, sesame oil, brown sugar, chili paste, and mirin. Process to form a smooth paste, then transfer to a zip-top plastic bag. Add the chuck roast, seal the bag, and move the roast all around until it's completely coated with the marinade. Refrigerate overnight.
Remove the bag from the refrigerator and let the roast come to room temperature, which will take 1 to 2 hours. Remove it from the bag, reserving the marinade. There's no need to pat the roast dry.
Preheat the oven to 350 degrees F.
Heat the vegetable oil in a large, heavy-bottomed Dutch oven over medium-high heat until really hot. Add the beef and sear it until well browned and crusty on all sides, 10 to 12 minutes total. Add the reserved marinade, cover, and place in the oven. Cook until you can pull the roast apart with a fork with no resistance, 2 1/2 to 3 hours.
Transfer the beef to a cutting board and pull it into shreds with two forks. Return the shredded beef to the pot and cover to keep warm.
Prepare the tacos by placing 1/4 cup of the beef on each warm tortilla, and top as desired with the pickled cucumbers, coleslaw, and cilantro. Drizzle with Sriracha, if desired. Fold and feast.