Place the sliced tomatoes on a baking sheet lined with foil, and spray with olive oil. Roast the tomatoes under a broiler until they start to bubble.
Saute the onion, bell pepper and garlic in the instant pot with olive oil until the onions are translucent.
Add the rest of the ingredients the Instant Pot except the tomatoes, and stir well.
Pour the tomatoes on top and do not mix. This is to prevent any chance of them burning and sticking to the bottom.
Cook on High Pressure for 10 minutes, allowing it to release pressure naturally.
After the pressure has come down, use an immersion blender to purée the sauce until smooth.