Combine the chicken, soy sauce, dark soy sauce, honey, mirin, ginger paste, and garlic paste in a slow cooker.
Cook on high for 4-5 hours or low for 5+ hours.
In a small bowl, mix the cornstarch and cold water to make a slurry. Add the slurry to the slow cooker and let sit uncovered for 15-20 minutes to thicken the sauce.
Cook the rice according to package instructions.
In a separate bowl, mix the mayo, greek yogurt, sriracha, salt, pepper, and garlic powder. Add milk as needed to reach desired consistency.
Serve the chicken and rice together, topped with the yum yum sauce and chopped green onions.
