Bring a large pot of salted water to a boil. Set up an ice bath nearby. Place half of the broccoli rabe into the boiling water and cook for 1 minute, then remove with tongs to the ice bath to stop cooking. Repeat with remaining broccoli rabe. Place broccoli rabe into a large colander to drain.
Preheat an outdoor grill for medium-low heat, and lightly oil grate.
Whisk together olive oil, lemon juice, crushed red pepper flakes, and salt in a small bowl. Toss drained broccoli rabe with oil mixture, then place onto hot grate.
Grill, turning occasionally, until thick stems have softened, 8 to 10 minutes. Remove thinner leafy pieces as they become done to prevent burning. Remove to a serving platter.