Heat olive oil over medium heat in a medium sauté pan. Add sausage; brown well. Add tomato paste; cook 5 minutes until brown. Add onions, celery, garlic, carrots, and oregano. Cook until garlic is aromatic, approximately 5 minutes. Pour into a 4-quart slow cooker. Add tomatoes and chicken stock. Cook on low setting for 6–7 hours or until the vegetables are tender. Stir in beans, zucchini, spinach, and cooked pasta. Cook on high setting for 8 minutes or until beans and pasta are warmed through and spinach has wilted. To Serve: Pour the soup into a bowl. Top with a little pesto and fresh grated parmesan cheese. Serves 7 to 9.