In a medium bowl, whisk together the low sodium soy sauce, water, rice vinegar, brown sugar, minced garlic, and grated ginger until well combined.
Turn your Instant Pot to the sauté setting. Add the chicken pieces and cook for 2-3 minutes until they are lightly browned.
Pour the teriyaki sauce over the sautéed chicken in the Instant Pot. Stir to ensure all the chicken pieces are well-coated in the sauce.
Close the lid of the Instant Pot, ensuring the valve is set to sealing. Set it to cook on high pressure for 8 minutes.
Once the cooking time is up, carefully perform a quick release by turning the valve to venting.
In a small bowl, mix the cornstarch with 1 tablespoon of water until smooth. Stir this mixture into the pot with the chicken. Turn the Instant Pot back to sauté mode and cook for another 2-3 minutes until the sauce thickens.
Stir in the broccoli florets and cook for an additional 2-3 minutes until they are bright green and tender-crisp.
Scoop the teriyaki chicken and broccoli onto plates. Top with sliced green onions and a sprinkle of sesame seeds.