Heat a large pot over medium-high heat. Add the oil. When hot, add the diced onion, garlic, carrot, celery, red bell pepper, and parsnips. Sauté for 3-4 minutes. Add the diced tomatoes or crushed canned tomatoes and bring to a simmer.
Cook for about 5 minutes and add the stock and parmesan rind if using. Bring back to a simmer and allow to cook for 10 minutes, or until the vegetables are soft.
Add in the cooked rice, leftover meat if using, and the chopped kale. Bring back to a simmer and cook for another 2 minutes.
Season generously with salt and pepper. Serve hot or store in the fridge for 3-4 days.
Note: If you have it, a dollop of Pesto on top would make this soup extra special!