Wash Swiss chard and cut into 1-inch strips. Separate the thick, tough stalk sections from the upper leafy strips.

Add 1 tablespoon salt to 1 cup water in a large saucepan; bring to a boil. Add stalks and cook for 2 minutes. Stir in leafy strips. Cook until stalks are fork-tender and leafy strips are wilted, about 6 minutes. Drain.

Heat oil, garlic, and red pepper flakes in a large skillet over medium heat until aromatic, about 3 minutes. Add drained Swiss chard; cook and stir for 2 minutes. Season with salt to taste.