In a large skillet - Add oil, onion, carrot, bell pepper, and celery. Season with one tsp. salt and one tsp. black pepper. Sauté for 5 minutes, then add vinegar and continue cooking for 2-3 more minutes.
Add cauliflower and mushrooms and mix well to combine. Season with 2 tsp. salt and poultry seasoning. Cook until tender, 5-7 minutes more, stirring frequently.
Add parsley, rosemary, and vegetable broth and mix well. Cover and cook for about 10 minutes (or until vegetables reach desired tenderness), stirring occasionally.