Cut off the tough stems from the Swiss chard leaves, including 1 - 2 inches into the leaves; discard the stems. Wash the leaves well, drain and shake off excess water. Pile the leaves flat and slice into strips 1 inch wide. Set aside.

In a large sauté pan or saucepan over medium heat, melt the butter. Add the onion and cook gently until translucent, 3 - 4 minutes. Add the ham and cook for another 3 - 4 minutes, stirring frequently. Add the Swiss chard, reduce the heat, cover and cook for about 10 minutes. Remove the cover, stir and check for doneness by tasting a piece of ham; it should be tender to the bite. If more cooking is needed or too much liquid has collected, raise the heat and cook, uncovered, for 1 - 2 minutes.

Season to taste with salt and pepper. Using 1 of the lemons, squeeze in juice to taste. Transfer to a serving dish. Cut the remaining lemon into wedges for garnish.