Prep the sauce. In a bowl, whisk the pineapple juice from the can (reserve the chunks), soy sauce, ketchup, honey, vinegar, ginger, garlic, and sriracha if using.
This is your sweet-tangy base.
Layer the crockpot. Add sliced onion and bell pepper to the bottom. Place chicken on top. Scatter the pineapple chunks over the chicken.
Pour and cook. Pour the sauce evenly over everything.
Cover and cook on Low for 4–5 hours or High for 2.5–3.5 hours, until the chicken is tender and cooked through.
Shred or slice. Remove the chicken to a plate. Shred with two forks or slice into bite-size pieces. Skim any excess fat from the crockpot if needed.
Thicken the sauce. In a small cup, stir cornstarch with water to make a slurry.
Stir it into the hot sauce in the crockpot. Switch to High and cook 10–15 minutes until the sauce turns glossy and slightly thick. Stir in sesame oil for richness.
Return the chicken. Add the chicken back and toss to coat in the sauce.
Taste and adjust with a splash of soy for salt or honey for sweetness.
Serve. Spoon over hot rice. Garnish with sesame seeds and green onions for crunch and color.