Place chicken breasts in the slow cooker or Instant Pot.

Top chicken with the chopped onion.

In a small bowl, mix together the pineapple, 1/4 cup water, garlic, soy sauce, ketchup, honey, sesame seeds, and red pepper flakes. Pour the pineapple mixture over the chicken and onions.

Allow to slow cook for 4-6 hours on the LOW setting.

Once chicken is fully cooked, transfer the chicken from slow cooker/Instant Pot to a plate and cut or shred the chicken.

IF USING AN INSTANT POT, set the IP to the sauté setting. While the sauce is heating up, mix together the cornstarch and remaining 1/4 cup water. Add the cornstarch mixture to the Instant Pot and allow to cook until boiling, stirring frequently, about 6 minutes, or until thickened. Once sauce is thickened press cancel on the IP.

-OR-

IF USING A SLOW COOKER, transfer sauce to a sauce pan and bring to a boil. While the sauce is heating up, mix together the cornstarch and remaining 1/4 cup water. Add the cornstarch mixture to the sauce pan and allow to cook until boiling, stirring frequently, about 6 minutes, or until thickened. Remove from heat once the sauce is thickened.

Meanwhile, steam broccoli in a steamer or cook it until soft in a large pot with boiling water and drain.

Stir chicken in with the thickened honey sesame sauce.

Plate 1 cup steamed broccoli with 1/2 cup honey sesame chicken mixture.

As an optional step, you can top this with sliced green onion and extra sesame seeds.