Stir the ketchup, soy sauce, honey, garlic, oil, and onion together to make a mixture.

Place the chicken breasts in the crockpot and pour the mixture over them. Ensure the chicken is well coated.

Heat the chicken until it is thoroughly cooked. This can be done on a high or low setting. Cook on low for approximately 3-4 hours or on high for 90-150 minutes.

After it is cooked through properly, remove the chicken from the crockpot while leaving the sauce inside.

Take 3 tablespoons of water and dissolve 3 teaspoons of corn starch into it. Once combined, pour this into the crockpot and stir into the sauce.

Place the lid onto the crockpot and cook it on high for approximately 10 minutes or until the sauce condenses.

When the sauce has slightly thickened, return the chicken to the crockpot after cutting it into bitesize pieces. Make sure these are again well-coated in the sauce.

The chicken can then be served or left a while to simmer on low. Once ready, sprinkle with sesame seeds. This dish is best served over rice.