Gather and prep calmly. Set out all your ingredients to avoid surprises mid-step. Chop the onion, mince the garlic, and measure the pineapple juice and condiments. If using bell peppers or pineapple chunks, chop those now.

In a medium bowl, whisk together pineapple juice, brown sugar, ketchup, gluten-free soy sauce or tamari, minced garlic, Worcestershire sauce, salt, pepper, onion powder, and optional ground ginger until well blended.

In a skillet over medium-high heat, melt the butter. Add the onion and cook until softened and golden, about 6–8 minutes. Sprinkle flour over onions and stir for 30–60 seconds.

Pour the pineapple juice mixture into the skillet and bring to a gentle boil. Reduce heat and let it simmer for 10–15 minutes, stirring occasionally.

Place the chicken breasts in the slow cooker and pour the thickened sauce over them. Cover and cook on LOW for 8 hours or HIGH for 4–5 hours.

Once cooked, shred the chicken and return it to the slow cooker, mixing it with the sauce.

Spoon the Hawaiian chicken over rice or pile it in gluten-free buns. Garnish with chopped green onions and sesame seeds.