Cut the chicken into bite-size pieces. Season with salt and pepper.
Set Instant pot to Saute and add olive oil.
Add onion and cook on "saute" for a few minutes until almost caramelized.
Add garlic and cook for 1 more minute.
Add chicken and toss to coat with oil. Pour in the stock.
Close the lid and cook at high pressure for 7 minutes.
Once done, do a quick pressure release and open the lid.
In a cup, combine cornstarch with 1/2 cup of cooking liquid and make a slurry.
On the Instant Pot, press "saute" and pour the slurry over the chicken while stirring well.
Add broccoli and close the Instant pot. Let the broccoli for 5-6 minutes on saute. (NO need for pressure cooking).
Open the lid, mix a bit and serve :]