1. In a large pot, heat 1/4 cup plus 2 tablespoons of the olive oil. Stir in the garlic and cook over moderately high heat until lightly golden, about 1 minute. Add the chard leaves in large handfuls, allowing each batch to wilt slightly before adding more. Season the chard with salt and pepper and cook, stirring, until the leaves are softened and most of the liquid has evaporated, about 8 minutes. Transfer the chard to a bowl. Wipe out the pot.
2. Add the remaining 2 tablespoons of olive oil to the pot. Add the chard ribs and cook over moderately high heat, stirring occasionally, until crisp-tender, about 5 minutes. Stir in the wilted chard leaves and season with salt and pepper. Transfer to a bowl, sprinkle with the lemon zest and serve right away.