Make the sauce base: In a bowl, whisk soy sauce, water or broth, brown sugar, rice vinegar, sesame oil, garlic, and ginger until the sugar dissolves.
Load the crockpot: Place the chicken in the slow cooker and pour the sauce over the top, making sure the chicken is coated.
Cook low and slow: Cover and cook on Low for 4–5 hours or on High for 2–3 hours, until the chicken is very tender and easily shreds.
Thicken the sauce: Transfer about 1/2 cup of the cooking liquid to a small bowl.
Stir in the cornstarch slurry (2 tablespoons cornstarch + 2 tablespoons water) until smooth, then pour it back into the slow cooker. Stir gently. Cover and cook on High for another 15–20 minutes, until the sauce is glossy and thickened.
Shred the chicken: Remove the chicken to a plate and shred with two forks.
Return it to the slow cooker and toss to coat in the sauce.
Prep the bowls: While the sauce thickens, cook your rice and steam your veggies until just tender. Aim for crisp-tender broccoli and peppers so they keep a little bite.
Assemble: Scoop rice into bowls, top with teriyaki chicken, and add veggies. Spoon extra sauce over the top.
Finish with toppings: Add green onions, sesame seeds, and a pinch of red pepper flakes if you like heat.
A squeeze of lime brightens everything up.