Season the chicken breasts generously with salt, black pepper, garlic powder, and onion powder. In a skillet over medium-high heat, add the olive oil. Once hot, sear the chicken for about 3-4 minutes on each side until browned but not cooked through.
In a medium bowl, whisk together the pineapple juice, soy sauce, brown sugar, cornstarch, rice vinegar, grated ginger, and crushed red pepper flakes (if using) until smooth.
Place the seared chicken in the crockpot and pour the sauce mixture over the chicken.
Cover and cook on low for 6 hours or until the chicken is tender and fully cooked.
Once done, shred the chicken in the sauce and mix well.
Serve the chicken over cooked rice or quinoa, garnished with diced fresh pineapple, chopped green onions, and sesame seeds.