Cut the chicken thighs into 1-inch chunks and season them evenly with salt and black pepper. Dice the onion into 1/2-inch pieces and chop the bell pepper into similar-sized pieces. This even sizing ensures everything cooks at the same rate. Mince the fresh ginger and garlic cloves finely so they distribute their flavor throughout the sauce. Having all your prep work done before adding ingredients to the slow cooker makes the assembly seamless.

In a medium bowl, whisk together the brown sugar, honey, soy sauce, minced ginger, minced garlic, toasted sesame oil, and red pepper flakes. Stir until the sugar dissolves and the mixture is well combined. This creates a balanced sauce with sweet, salty, and spicy notes that will infuse the chicken and vegetables as they cook.

Add the seasoned chicken chunks to your slow cooker, then layer in the diced onion and chopped bell pepper. Drain the pineapple tidbits, reserving the juice, and add the fruit to the slow cooker. Pour the sauce from Step 2 over everything, then add the reserved pineapple juice. Stir gently to combine all ingredients, ensuring the sauce coats the chicken evenly.

Cover the slow cooker and cook on LOW for 5 hours, or on HIGH for 3 hours if you're short on time. The chicken will become tender and absorb all the sweet and savory flavors. I prefer cooking on LOW because it gives the flavors more time to develop and keeps the chicken juicier. You'll know it's done when the chicken is fork-tender and the sauce is fragrant and slightly reduced.

While the chicken is still cooking or just after it finishes, mix the cornstarch with cold water in a small bowl, stirring until no lumps remain. This creates a slurry that will thicken the sauce without making it cloudy. Stir this mixture into the slow cooker, distributing it evenly throughout the liquid.

Continue cooking for 30 minutes more on HIGH heat (or switch to HIGH if still on LOW) to allow the cornstarch to activate and thicken the sauce to a light glaze consistency. The sauce should coat the back of a spoon lightly when ready. Taste and adjust seasonings if needed—add more soy sauce for saltiness or a pinch of red pepper flakes for heat.

For immediate serving, spoon the Hawaiian chicken over cooked rice and garnish with sesame seeds or sliced green onions if desired. To freeze for a freezer meal, let the mixture cool to room temperature, then transfer to freezer-safe containers or bags. It will keep for up to 3 months. When ready to reheat, thaw overnight in the refrigerator and warm in a slow cooker on LOW for 2-3 hours, or in a skillet over medium heat until heated through.