1. Remove stems from chard leaves. Cut leaves into wide ribbons; slice stems. Keep leaves and stems separate.
2. Heat oil in large skillet over medium heat; cover. When hot, add shallots and sugar; cook 1 minute. Stir in orange; reduce heat to low, stirring frequently until shallots and orange are caramelized (about 10 minutes). Add vinegar.
3. Return heat to medium; stir in chard stems. Cook until softened, stirring frequently (1-2 minutes). Add chard ribbons; cover and let steam 2-3 minutes, stirring frequently. Turn off heat; re-cover pan 2-3 minutes. Sprinkle with salt and pepper, stirring frequently. Sprinkle with pistachios; serve hot or at room temperature.