In a large saucepan over medium high heat, cook the sausage until browned and broken into small pieces. Set aside on a plate.
Add the olive oil to the saucepan, then add the mushrooms and garlic. Cook until the mushrooms begin to soften, about 3 to 5 minutes.
Add the onion, bell pepper, and zucchini, and cook while stirring occasionally until veggies are tender-crisp.
Stir in the diced tomatoes, broth, apple cider vinegar, tomato paste, and spices. Add the sausage back to the soup. Bring to a boil, then reduce to a simmer.
Cook covered on low heat for at least 30 minutes or up to 2 hours for the flavors to combine.
Season with additional salt & pepper to taste, and stir in chopped spinach or kale before serving.