Heat a large skillet over high heat and add a small amount of oil; once hot, sear the chicken pieces in batches until browned on all sides.
Place the seared chicken in the slow cooker.
In the same skillet or a bowl, combine 1/3 cup soy sauce, 2 tablespoons lime juice, 1/4 cup orange juice, 1 tablespoon lime zest, 2 tablespoons sesame oil, the entire can of pineapple with juice, bell peppers, 1 tablespoon minced garlic, 1 tablespoon grated ginger, 1/3 cup brown sugar, 1/3 cup hoisin sauce, and red pepper flakes if using; stir to combine.
Pour the sauce and pineapple mixture over the chicken in the slow cooker and cover with the lid.
Cook on LOW for 7–8 hours or HIGH for 3–4 hours until the chicken is tender and cooked through.
About 30 minutes before the end of cooking, whisk 2 tablespoons cornstarch with 4 tablespoons orange juice until smooth, then stir the slurry into the slow cooker; replace the lid and continue cooking 30 minutes to thicken the sauce.
When done, check the seasoning and shred or chop the chicken if desired; garnish with sliced green onions, sesame seeds, and slivered almonds, and serve warm.
