2 tablespoons olive oil
1 large onion, diced (divided)
8 oz (225 g) button mushrooms, quartered
4 cloves garlic, minced
1 teaspoon minced fresh rosemary
1 teaspoon minced fresh thyme
4 cups (.95 liter) low-sodium beef stock
1 teaspoon Worcestershire sauce
1 bay leaf
1/4 teaspoon salt
1/8 teaspoon black pepper
2 large stalks celery, chopped
2 large carrots, chopped
3/4 lb (350 g) cooked, cubed pot roast (about 3 cups)
1/2 cup (70 g) frozen green peas, thawed
1 teaspoon arrowroot starch, dissolved in 1 tablespoon cold water to make a slurry (see Note below)
2 tablespoons minced fresh parsley, for garnish