01 - Pat the beef chuck roast dry with paper towels and season generously on all sides with sea salt and freshly ground black pepper.
02 - Heat olive oil in a large skillet or Dutch oven over medium-high heat. Sear the beef on all sides until deeply browned, approximately 3 minutes per side.
03 - Transfer the seared beef to a slow cooker. Scatter the thinly sliced onion, minced garlic, and chopped red chili pepper around and over the meat.
04 - In a mixing bowl, combine the crushed pineapple with its juice, tomato puree, brown sugar, apple cider vinegar, soy sauce, ground cumin, and smoked paprika. Stir until well blended, then pour the sauce evenly over the beef.
05 - Cover and cook on low for 6 hours (or on high for 3 to 4 hours) until the beef is fork-tender and pulls apart with minimal effort.
06 - Remove the beef from the slow cooker and shred it using two forks, pulling the meat along the grain. Return the shredded beef to the pot and toss thoroughly with the sauce.
07 - Lightly toast the sandwich buns in a dry skillet or under the broiler until golden on the cut sides.
08 - Pile the saucy pulled beef onto the toasted buns. Top each sandwich with shredded red cabbage and fresh cilantro leaves. Spread mayonnaise or aioli on the bun if desired. Serve immediately.