Add olive oil to the Instant Pot. Using the display panel select the SAUTE function.
When oil gets hot, add onion to the pot and saute until lightly browned, about 7 minutes. Add garlic and cook for 1-2 minutes more.
Add broth to the pot and deglaze by using a wooden spoon to scrape the brown bits from the bottom of the pot.
Add chicken in an even layer. Add tomatoes in an even layer. Drizzle with balsamic vinegar and crushed red pepper (optional). Sprinkle with kosher salt and pepper.
Turn the pot off by selecting CANCEL, then secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- buttons and program the Instant Pot for 12 minutes.
When the time is up, quick-release the pressure. Sprinkle the mozzarella cheese and basil over the chicken, then cover 4-5 minutes until cheese melts.
Serve over zoodles, quinoa, brown rice or polenta.
Notes
*The MANUAL and PRESSURE COOK buttons are interchangeable.