01 - Pat the chuck roast dry with paper towels. 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 a deep golden-brown crust forms, approximately 3 minutes per side.
03 - Transfer the seared beef to a slow cooker. Scatter the thinly sliced onion, minced garlic, and chopped chili pepper around and over the roast.
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. Whisk until well blended, then pour the sauce evenly over the beef and aromatics.
05 - Cover the slow cooker 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 place it on a cutting board. Shred the meat using two forks, discarding any large pieces of fat. Return the shredded beef to the slow cooker and toss thoroughly with the sauce.
07 - Lightly toast the sandwich buns in a dry skillet or under a broiler until golden at the edges, about 1 to 2 minutes.
08 - Mound the saucy pulled beef generously onto each toasted bun. Top with shredded red cabbage and fresh cilantro leaves. Spread mayonnaise or aioli on the bun if desired. Serve immediately.