Dice the celery, onion, and carrot. Mince the garlic. Sauté these ingredients (without oil) for about 10 minutes in a large deep pan or pot. If the vegetables begin sticking to the pan, use a small amount of vegetable broth or water, adding more as needed.
While the celery, onion, carrot, and garlic are on the stove, peel and chop the potatoes into the size you desire. I use fairly large chunks (see image in post above).
Mix in the Italian seasoning, then add mushroom broth, potatoes, lentils, tamari, and pepper to the pot on the stove. Stir the ingredients together, then cover the pot with a lid. Bring to a boil, then lower the heat and simmer for about 25 minutes. Check to ensure that it doesn’t boil over, but it should be fine.
After about 25 minutes, mix in the frozen peas and corn.
If you want your stew to be thicker, do the following: In a small bowl, mix the cornstarch (or brown rice flour) and water until a smooth, white liquid forms. Then pour this mixture into the pot on the stove and mix it in. This will allow the stew to thicken up. Let sit for about 5 more minutes on low heat (stirring occasionally), or until your desired texture is reached.