Trim 1/2 inch off the ends of the broccoli rabe. Prepare a large pot of salted boiling water and a large bowl of ice water. Drop the broccoli rabe into the boiling water and blanch for 2 minutes. Remove and immerse in the ice water long enough to cool, about 15 seconds. Drain and place on paper towels to dry.

Heat the oil in a large skillet over medium heat. Stir in the garlic and cook for 30 seconds, then stir in the red pepper flakes. Add the broccoli rabe and sauté, shaking the pan and gently tossing so that it cooks evenly, until tender, especially the stems, for 3 to 5 minutes. Remove from the pan and drain off any excess liquid. Season with salt and pepper to taste, squeeze with lemon, and serve as a side dish.