Take the stems out of the mushrooms and place them into a food processor. Chop the mushrooms into a very fine dice like a small meat crumble. Do not make the pieces too small, however, because they will shrink during the cooking process.
Preheat an Instant Pot on the Saute setting until it says HOT. Add in avocado oil and swirl it around with a spoon to coat. Add in the diced white onion, diced red bell pepper, and diced celery. Cook until the onion is translucent, about 30 seconds to 1 minute. Add a ¼ tsp of kosher salt and stir well.
Add the mushrooms to the Instant Pot and stir well. Cook until the mushrooms start to smell browned. Add in the garlic powder then apple cider vinegar.
Add in the fire-roasted tomatoes, coconut aminos, and vegetable broth. Set the Instant Pot to high pressure and set for 1 minute. Once the time has elapsed, release the pressure. Taste and adjust any of the seasonings as desired. Serve immediately.