Add the diced onion, garlic and olive oil to the instant pot and press the saute function. Saute for 5 minutes or until the garlic starts to brown. Add in the bell pepper, carrot, celery and serrano pepper. Saute an additional 5 minutes.
Add in all remaining ingredients and stir to combine.
Set the instant pot to manual high pressure for 10 minutes and put the lid on sealing. It'll take about 10 minutes to come to pressure.
When it's done, let it release naturally for 10 minutes, then carefully set the valve to venting and remove the lid when it finishes releasing.
Stir well, then taste and adjust flavors as desired. Transfer 3 cups worth to a blender and blend until mostly smooth with a few chunks. Transfer back and stir. Serve with fresh cilantro, sour cream, avocado, chips and/or cornbread!