In a large nonstick skillet over medium heat, warm 2 tablespoons of the low-sodium vegetable broth.
Add the mushrooms and cook for about 4 to 6 minutes, or until mushrooms start to brown.
Add the onions to the skillet and cook for about 6 to 8 minutes, or until softened.
Add the garlic to the skillet and cook for 30 seconds to 1 minute, until fragrant.
Transfer the mushrooms, onions, and garlic to the slow cooker.
Add to the slow cooker the sweet potato, butternut squash, the rest of the vegetable broth, chickpeas, diced tomatoes, tomato paste, bay leaves, dried sage, dried thyme, and freshly cracked black pepper, to taste. Stir well.
Cover the slow cooker and cook on Low for 6 hours. Feel free to cook it for up to 8 hours.
About 15 minutes before you are ready to serve, lift the lid of the slow cooker and stir in the spinach.
Remove the bay leaves. Add ½ teaspoon balsamic vinegar. Taste and add an additional ½ teaspoon balsamic vinegar and/or additional black pepper, if desired. Serve hot. Enjoy!