Trim the stems off of the leaves (about 1-2 inches) and wash the rabe a few times. Once the water is boiling, add in the broccoli rabe and cook until tender, about 3-5 minutes. Drain the greens in a colander.
In a large pan, heat your 1 tbs olive oil on medium. Add in the garlic and chili flakes and stir for 30 seconds. Stir in the broccoli rabe and sauté for 1-2 minutes. Season with salt and pepper to taste. Remove promptly and transfer to your platter. Top with grated parmesan, drizzle with more olive oil and serve with lemon slices.