Assemble your ingredients. Wash the mushrooms and celery in a colander and let drain. Peel Parsnips and carrots and roughly chop into bite-sized pieces. I personally like big, chunky vegetables, but if you are cooking for kids, you may want smaller pieces.
Cut up celery by slicing lengthwise into 4 pieces, and then cutting crosswise into thick, short chunks. The onions I had were small, so I just cut them in half, cut off the top and stem, and then peeled the outer layer. If your onions are bigger, you can cut them into smaller pieces. Chop or mince the garlic.
Turn your Instant Pot on to "sauté", and add the olive oil, let heat for a few minutes. Add half the meat and quickly brown, removing the first half to a small bowl before browning the second half. Don't let the meat overcook. You are just wanting to put a bit of a sear on the meat, not cook it. Remove all meat to the bowl.
In the Instant Pot, dump all the chopped vegetables and stir around, coating them with the meat juices and browned bits. Add the bone broth and scrape around the bottom of the bowl with a silicone spatula. Turn off sauté.
Add tomato paste, chopped tomatoes, and give it a stir. Add meat back in, along with the parsley, oregano, salt, and pepper. Give it all a stir.
Close the lid, shut the vent, and set to Manual, high pressure for 5 minutes. When the time is up, do a natural pressure release for 10 minutes, If the pin hasn't dropped, do a controlled release of the valve (turning part-way with a spoon or silicone glove. If soup begins to splatter, close the valve and open slowly again. This will minimize any splatter mess.).
Turn off the pot, and carefully open it. Give the soup a stir. Serve in a bowl, top with some fresh chopped parsley, if you want to be fancy. Enjoy!
Remove the inner pot and place on trivet to let cool. Soup will be very hot, so be careful. Once the soup has cooled down, I like to transfer it to a storage container to keep it in the fridge. I can then grab a bowl for dinners over the next few days. You can also transfer to small freezer-to-microwave bowls if you want to freeze in portions that can be heated up later.