Heat olive oil over medium-high heat. Add shallot, pistachio nuts and chard stems. Cook until the shallot is soft and begins to brown. Add the chard leaves and stir to coat in oil. Lightly sprinkle with salt and pepper. Cover and cook for 1-2 minutes, until the chard is wilted, Uncover, stir, and continue to cook for 7-9 minutes, until the stems are tender.
Stir in the mint. Continue cooking 1-2 minutes, until the flavors are combined.