Saute onion, bell pepper, and celery in oil in large saucepan untill onion is tender, about 5 minutes. Stir in 3 cups stock; heat to boiling. Mix remaining 2/3 cup stock and flour; stir into boiling mixture. Boil, stirring constantly, until thickened, about 1 minute.
Stir potatoes, squash, zucchini, mushrooms, peas, and herbs into stew. Simmer, covered, until vegetables are tender, 10 to 15 minutes. Season to taste with salt and pepper.
RECOMED: Topping with Herb Dumplings.
Spoon dumpling mixture on top of stew in 6 large spoonfuls; cook over low heat, uncovered, 10 minutes. Cook, covered, 10 minutes longer or until dumplings are tender and pass the toothpick test.