Add frozen seasoning blend to Instant Pot and set it to sauté on a low setting. Stir the seasoning blend and sauté until it begins to brown, about 5 minutes. Add the fresh mushrooms and garlic and sauté for another 2 minutes.
Add all of the remaining ingredients except for nutritional yeast and stir well. Lock the lid on the pot and set it to pressure cook for 12 minutes.
After the IP has indicated that 12 minutes of pressure cooking have been completed, open the valve to release the pressure manually. Stir in the nutritional yeast. If the soup seems too dry, add extra water. Taste it to check the seasoning and add more herbs if desired. Keep warm until ready to serve.
Stove Top
Heat a 5-6 quart saucepan and add frozen seasoning blend. Stir the seasoning blend and sauté until it begins to brown, about 5 minutes. Add the fresh mushrooms and garlic and sauté for another 2 minutes.
Add all of the remaining ingredients except for green beans and nutritional yeast. (Use 6 cups of water.) Bring to a boil, reduce heat to low, and cover the pot. Cook for 15 minutes and then add the frozen green beans.
Cook for another 15 minutes and then check the lentils to see if they are tender. If not, continue cooking until tender.
Stir in the nutritional yeast. If the soup seems too dry, add extra water. Taste it to check the seasoning and add more herbs if desired. Keep warm until ready to serve.
Notes
I used frozen seasoning blend as a time-saver. It is mostly chopped onions with some celery, red bell pepper, and parsley added. You can make your own or substitute one large onion, chopped.
Other brands of dried shiitakes will work. Follow package directions for rinsing (some of them are gritty unless rinsed) and chop or tear them into small pieces.
The two types of bouillon I use most often are Edward & Sons Not-Chick'n and Better Than Bouillon No Chicken Base. Whatever bouillon you use, use the amount that will flavor 4 cups of water. For Edward & Sons, that is two cubes. For Better Than Bouillon, it's 4 teaspoons. Or you could use vegetable broth instead of water, but I find that more expensive.
Sodium is high because of the bouillon I used. You can reduce it by eliminating the salt and/or bouillon or using a lower-sodium bouillon.