In a large skillet, heat a drizzle of olive oil over medium-high heat. Add the sliced smoked andouille sausage and cook for about 3-4 minutes, or until the sausage is lightly browned and fragrant.

Once the sausage is browned, stir in minced garlic, diced onion, diced carrots, and diced celery. Sauté for another 3-4 minutes until the vegetables are slightly softened and the onions are translucent.

Transfer the sautéed mixture into a 6-quart slow cooker. Add the drained and rinsed Great Northern beans, dried oregano, and bay leaves. Season generously with kosher salt and freshly ground black pepper.

Pour in 4 cups of chicken broth and 2 cups of water into the slow cooker, stirring gently to combine all the ingredients.

Cover the slow cooker and set it to cook on low heat for 7 to 8 hours, or on high heat for 3 to 4 hours, until the vegetables are tender.

About 10 minutes before serving, stir in the fresh baby spinach into the soup. Cover again and allow the spinach to wilt and soften.

Once everything is cooked and the spinach has wilted, ladle the soup into bowls. Top each serving with a sprinkle of shaved Parmesan cheese for added richness.