Cook the potato in water to cover until tender, but not soft, about 4 minutes.
Drain and reserve in a bowl.
In a large saucepan, heat 1 tablespoon of the oil over medium heat and cook the onion, garlic, and jalapeño until the onion is translucent, 3 to 4 minutes.
Add the chard, pushing it down into the pan.
Add ⅓ cup water.
Cover and cook, stirring once or twice, until the chard is wilted and tender, 8 to 10 minutes.
Add the reserved cooked potato, the remaining oil, salt and pepper.
Stir to mix.