Place bacon in a large skillet over medium-low heat; cook and stir until browned, about 5 minutes. Add onion and garlic; cook, stirring constantly, 1 minute more.
Place chard into skillet; sprinkle with salt. Cover and reduce heat; cook until tender, about 10 minutes. Turn chard with tongs to distribute onions and garlic; cook, covered, until flavors meld, 3 to 5 minutes more.