Heat oil in a large skillet over medium heat. Add onion and chard stems and cook, stirring often, until softened, 3 to 5 minutes. Add tomato, broth (or water), chipotle to taste and salt; bring to a simmer. Add chard leaves and cook, covered, stirring once, until just tender, about 2 minutes. Scatter cheese evenly over the chard and cook, uncovered, until the cheese is melted, 1 to 2 minutes more. Serve immediately.