Heat the olive oil in a large saucepan over medium-low heat. Add onion, garlic, carrot, celery and thyme. Cook, covered, for 10 minutes, stirring occasionally, until softened. Add the canned tomatoes to pan with 3 cups of water. Increase the heat to high and bring to the boil.
Reduce heat to low. Add the couscous to pan and simmer for 5 minutes, until couscous is tender. Add rinsed butter beans, kale and vinegar. Simmer soup for 2–3 minutes, or until kale has wilted. Divide the soup between 4 serving bowls and garnish with extra thyme. Serve with toasted wholegrain sourdough rolls.