In a large crock pot, place the chopped carrots, potatoes, and celery into the bottom of the pot.Put the ½ cup flour, season salt and pepper into a large ziploc bag. Add the cubed stew meat and shake the bag till all the meat is covered.Heat the olive oil in a large frying pan and cook the meat till browned.Move the meat to your crock pot and place on top of the vegetables. Meanwhile, fry the onion in the same frying pan till slightly tender.Add the onion to the crockpot.Sprinkle the onion soup over the top of the vegetables.Pour the broth and water over the onion soup making sure to cover all of it.Sprinkle the parsley flakes over the top.Cook on low for 6 hours.When there is about 1 hour left, slice the mushrooms and add them to the stew.After the mushrooms have cooked, add the thickening.To thicken the stew, mix the warm water and flour together in a small bowl. Add the thickening to the stew and stir in.Cook for another 15-20 minutes.