Add olive oil to the Instant Pot, and turn on the SAUTE setting. Add diced onion, and sauté for a few minutes until the onion is soft and translucent.
Add grated or diced garlic to the pot, along with all the seasoning. Sauté for another minutes, then turn the Instant Pot off.
Then, add the canned diced tomatoes, vegetable stock and fresh basil if using. Stir to combine the ingredients.
Important: Use a wooden spoon to scrape the bottom of the Instant Pot to remove any pieces of onion that might be stuck.
Seal the lid on the Instant Pot, and turn on the PRESSURE COOK or MANUAL setting for 5 minutes. The pot will take a few minutes to get to pressure before the timer starts counting down.
When the timer is up, allow the pressure to release naturally for about 10 minutes, then perform a quick release according to the manufacturer's instructions.
Use a hand blender to blend the soup smooth. Alternatively, use a regular blender, and add the soup in several batches until it's all smooth.
Season with additional salt and pepper to taste if needed, and serve.