Turn your Instant Pot to the sauté function and add a couple tablespoons of water or broth to the pot. Place the onion, garlic, peppers, mushrooms, walnuts and all the seasoning inside. Then sauté for 2-3 minutes, until slightly softened.
Add the remaining ingredients (broth, tomato sauce and rice), mix well and close the lid. Set the valve to the sealing position pressure cook for 22 minutes. (It will take about 8 minutes to build pressure before the pot begins counting down.) Once the timer is complete, let it naturally release for 10 minutes. Then quick release the remaining pressure and remove the lid when safe to do so. Enjoy.
Do not slice your veggies too thin. They will cook for a while in the pot, so they'll withstand cooking best, if they are thick cuts.Alternatively, if you prefer your veggies crisp, remove from the pot once sautéed, pressure cook your rice in the broth and tomato sauce, then add the veggies back in and mix well.Make sure to push down any loose grains of rice on the sides of your pot before pressure cooking. Everything should be covered in the liquid for even cooking.If you already released pressure and forgot to do a 10 minute natural release, just hit sauté and stirring often, continue cooking for 3-5 minutes to absorb excess liquid. Or, set aside for about 10 minutes or so. The rice will continue absorbing the liquid as it rests and cools.Leftovers keep refrigerated for up to 3 days, and you may reheat on stove top or in your Instant Pot.