Place all the ingredients, up to the chicken, in the Instant Pot and stir to combine. Lay the chicken breast on top.
Cover, set to sealing and cook on manual high pressure for 15 mins. Let steam release naturally when done.
Remove the chicken from the pot and shred it with 2 forks. Place it back into the pot.
Pour 1 cup of the soup (including any shredded chicken) into a high-powered blender and blend until smooth. Pour back into the soup.
Add the coconut milk, tahini and spinach and stir. You can cover the pot and turn to sautee mode for a few minutes to let the spinach wilt, if it doesn't on it's own.