Fill a large pot with water, salt generously, and bring to a boil. Trim half an inch off the tough ends of the broccoli rabe stems.
Add the broccoli rabe to the boiling water and blanch for 2–3 minutes, until the vegetable is bright green and just tender. Immediately transfer to a bowl of ice water to cool and stop the cooking process. Drain well and pat dry to prevent splattering.
Heat olive oil in a large skillet over medium heat. Add the garlic and cook for 30 seconds, stirring, until fragrant but not browned.
Add broccoli rabe to the pan. Season to taste with salt and pepper. Sauté, stirring and tossing occasionally, for 3–5 minutes, until the stems are tender and the greens are glossy.
During the final 1-2 minutes of sautéing, add the lemon to the skillet, cut side down.
For extra brightness, add the juice from the sautéed lemon over the broccoli rabe before serving. Taste, adjust salt and pepper if needed, and serve hot.