Separate the stems of the chard from the leaves. Cut the leaves into thin strips and set aside. Thinly slice the stems.
Heat the olive oil in a large skillet or pot over medium heat. Stir in the sliced garlic, red pepper flakes, and chard stems, and cook for 3 minutes until the flavor of the garlic mellows and the stems begin to soften. Stir in the shredded chard leaves, cover, and cook 5 minutes over medium-low heat. Stir, recover, and continue cooking until the chard is tender. Toss with lemon juice to serve.
