In a saucepan heat vegetable oil over medium heat. Add the onion, cover and simmer 5 minutes or until tender. Add the sliced mushrooms and saute 2 to 3 more minutes or until somewhat tender. Add the carrots, parsnips and broth. Bring to a boil and simmer 5 minutes or until the carrots are tender. Add the tortellini, cover and cook 8 minutes or until cooked through. While the vegetables and tortellini are cooking, roughly chop the spinach. When the tortellini is cooked through, stir in the spinach and simmer a minute or until tender. Season with salt and pepper and ladle into a soup bowl.