Put raisins and vinegar in a small bowl with 1/4 cup boiling water. Set aside to let soak 10 minutes.
Heat a large pot over medium-high heat. Drain and reserve raisins; add liquid to the pot. Add chard a few handfuls at a time, stirring and letting the chard cook down until all of it fits in the pot. Add onion and salt, lower heat to medium, cover and cook until onion and chard are tender, 10 to 12 minutes. Stir in raisins and cook 1 minute longer. Top with walnuts and serve.
Per Serving:70 calories (20 from fat), 2.5g total fat, 200mg sodium, 13g carbohydrates, (2 g dietary fiber, 8g sugar), 2g protein.
Note: We've provided special diet and nutritional information for educational purposes. But remember — we're cooks, not doctors! You should follow the advice of your health-care provider. And since product formulations change, check product labels for the most recent ingredient information. See our Terms of Service.