Bring a large pot of water to the boil and salt heavily. Rip the Swiss chard into large pieces and boil for one full minute in the water, until tender at the stem. Shock the Swiss chard in ice water, and drain, squeezing lightly to remove excess water.
In a large mortar and pestle crush the garlic clove and then add the sesame seeds, pounding to crack and release their fragrance. Add the red pepper flakes, sugar, soy sauce, and sesame oil and pound until combined. Add half of the Swiss chard and pound lightly to infuse with the aromatics. Add the rest of the Swiss chard, if it fits, or pour everything into a bowl and muddle the seasonings and greens until fully coated. Transfer the salad to a serving dish and chill before serving.