In the bottom of a slow cooker, combine the garlic, ginger, tamari, honey, ketchup, toasted sesame oil, and rice vinegar. Whisk until well combined.

Nestle the chicken breasts into the sauce and toss to coat. Sprinkle the chicken with salt and pepper. Cover and cook on low for 8 to 10 hours, or on high for 4 hours.

When the cook time is complete, use tongs to transfer the chicken to a baking sheet and set aside. Reduce the heat on slow cooker to keep warm.

In a small bowl, whisk together 2 tablespoons of water and the tapioca flour until well combined to make a slurry. Pour it into the slow cooker and stir until the sauce thickens slightly.

Next, using two forks, shred the chicken into bite-sized pieces. Transfer the shredded chicken back into the slow cooker and gently toss until it is well coated in the sauce.

Add the sesame seeds and gently toss once more. Let the chicken rest for about 10 minutes to allow the juices to settle and the sauce to absorb into the chicken.

To serve, spoon the chicken and sauce over prepared rice. Garnish with sliced green onions.