How to Make It
Heat the oil in a large skillet over medium heat. Add the mushrooms and ¼ teaspoon each salt and pepper and cook until the mushrooms are tender, 3 to 4 minutes.
Add the chestnuts and chard and cook until the chard is wilted, 2 to 3 minutes more.
Fold mushrooms, chestnuts, and chard into the stuffing mix and bake according to the package directions.