Saute leek and mushroom in oil in instant pot using the lower saute setting (can change it by hitting the adjust button a few times.
Add carrots, potatoes, celery, water, herbs, worcestershire sauce and salt and pepper. Stir well, then add water and stir again. Set instant pot to 13 minutes on Stew function (or less if you like your veggies less done).
Meanwhile, saute seitan in a skillet on the stove and set aside.
Do a 15 minute natural release then release the pressure, putting a towel over the valve if you want to contain the steam.
Open lid, add seitan, peas, and flour slurry, set to Saute and cook down a minute or two to thicken it a bit.