Preheat oven to 450°. Trim and discard chard stems; roughly chop leaves. Pour olive oil into a 10- to 12-inch frying pan over medium-high heat. When hot, add onion and stir often until softened, about 4 minutes. Add chard, sprinkle with nutmeg, and season to taste with salt and pepper. Stir until wilted, 3 to 5 minutes; set aside.
On a lightly floured surface, divide dough into four equal pieces. Using a lightly floured rolling pin or your hands, roll or stretch each piece into a 6-inch round. If dough shrinks, let it rest about 5 minutes, then roll again.
In a small bowl, mix ricotta, parmesan, dried tomatoes, pine nuts, and chile flakes (if using). Season with salt and pepper to taste. Mound equal portions of ricotta mixture in center of dough rounds. Top with chard mixture.
Gently pull half of dough over filling to make a half-moon shape. Fold bottom edge of dough over top edge and pinch firmly to seal. Brush tops of calzones lightly with olive oil. Transfer to a large baking sheet.
Bake calzones on middle rack until golden brown, 20 to 25 minutes (15 to 20 minutes in a convection oven). Let cool about 5 minutes, then transfer to plates.
Note: To make in advance, prepare through step 4, then freeze on a baking sheet. When frozen, wrap each calzone with aluminum foil and keep in freezer for up to 1 month. Bake at 375° for 30 to 35 minutes, until browned and cooked through.
Toasting nuts: Toasting nuts makes them crunchier and intensifies their flavor. In the case of thin-skinned nuts like hazelnuts or peanuts, it also makes removing their skins easier.
To toast a small amount: Place nuts in a small frying pan over medium-high heat and cook, stirring frequently, until they smell fragrant and turn a light shade of golden brown (they will continue to toast a bit more when removed from heat).
To toast larger batches: Spread the nuts in a single layer in a shallow baking pan and toast in a 375° oven for 10 to 15 minutes until the nuts are lightly browned and smell rich and toasty.
To skin nuts after toasting: Place them in a kitchen towel and rub vigorously. Most of the skins will fall right off. Don't worry if a few bits still cling here and there; they won't harm the flavor or texture.
Note: Nutritional analysis is per serving.