In a large pot over medium-high heat, add olive oil. Once hot, add sausage and cook 5-7 minutes, stirring occasionally, until nicely browned. Add onions and garlic; cook 2-3 minutes, until soft and fragrant.
Stir in thyme leaves, Italian seasoning, diced tomatoes, beans and chicken broth. Cover and bring to a boil. Reduce heat to low and simmer uncovered 25-30 minutes. Stir in spinach during last 5 minutes of cooking. Season with salt and pepper.
Spoon into serving bowls and top with grated parmesan cheese, if desired.