Push the SAUTE button on the Instant Pot.
Heat the oil in the bottom of the pot. Add in the diced onion and chicken and stir for a couple of minutes.
Add in the garlic and stir until the onions are translucent and the chicken starts to cook.
Now, add in the dried basil, tomato paste, chicken broth, petite diced tomatoes (with the juice), cheese tortellini, salt, and pepper.
Give a quick stir. Cover the Instant Pot and secure the lid. Make sure the valve is set to SEALING.
Press the MANUAL or PRESSURE COOK button and set the timer to 15 minutes.
Once the timer beeps let out the pressure by gently moving the valve to VENTING.
Stir in the spinach, Parmesan cheese, and half and half.
Turn the IP to saute to heat everything through.
Ladle the soup into bowls and serve.