Separate the stems of one bunch chard from the leaves. Cut the leaves into thin strips and set aside. Thinly slice the stems.
Heat 2 Tbsp. olive oil in a large skillet or pot over medium heat. Stir in 2 cloves sliced garlic, a pinch 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 1 tsp. lemon juice to serve.