Separate the stems of the chard from the leaves; cut leaves into thin strips and set aside. Thinly slice the stems.

Heat olive oil in a large skillet or pot over medium heat. Stir in garlic, red pepper flakes, and chard stems; cook and stir for 3 minutes until garlic mellows and stems begin to soften.

Stir in shredded chard leaves, cover, and cook 5 minutes over medium-low heat. Stir, re-cover, and continue cooking until chard is tender. Toss with lemon juice to serve.