Note: this recipe will work for 2 large chicken breasts sliced in half or 4 small chicken breasts (not cut in half).
Slice large chicken breasts in half, width-wise, to create 4 thin chicken breast halves.
Season all sides of the chicken with some salt and pepper.
Set Instant Pot on "saute" and let it heat through.
Add some olive oil to the pot and place chicken breast halves in it. Let chicken saute until it starts to brown on one side and flip them over. Let them saute until that side starts to brown and take chicken out.
Add garlic and saute until fragrant. Add marinara sauce and basil and stir well. Let it heat through and turn off the saute.
Nestle chicken back into the pot, in the middle of the sauce.
Close the lid and make sure it's latched. Turn the valve to "seal" and set the Instant Pot to pressure cook on LOW pressure for 3 minutes.
When it's done, turn it off, and carefully release the pressure on quick release. Add Mozzarella cheese, Parmesan cheese, and some basil over each chicken half.
Close the lid but do not turn on the Instant Pot. Just let the cheese melt in closed pot for 4-5 minutes. Take off the lid and serve right away.