Remove stems from chard and chop stems into ½-inch sections. Cut leaves into ½-inch strips. Julienne onion, cutting into strips that are approximately ⅛-inch thick.
Cut bacon into lardons roughly ¼-inch by ¼-inch by 1-inch thick. Place bacon in a large pan with a wide base, and cover with water. Put over high heat and cook until water has evaporated, and bacon is crispy.
In another large pan, heat oil over medium-high heat. Add onions and cook until they start to brown. Add the chard stems and cook for an additional 3 to 5 minutes. Add wine to deglaze the pan. Add chard leaves, and cook until wilted. Season mixture with salt and pepper.
To serve, place chard mixture on a platter and top with lardons.