Heat grill to medium (350°F to 450°F). Soak broccoli rabe in cold water to cover 10 minutes; drain. Grill broccoli rabe, uncovered, turning once, until florets are slightly charred and stems are tender-crisp, 3 to 4 minutes per side. Remove from grill, and set aside.
Heat 2 tablespoons of the oil in a large skillet over medium. Add garlic, and cook, stirring constantly, until light golden brown, about 1 minute. Add crushed red pepper, and cook, stirring constantly, until fragrant, about 30 seconds. Add broccoli rabe, and cook, stirring often, until warmed through, 1 to 2 minutes. Sprinkle with salt and black pepper, and transfer to a large platter. Top with feta, and drizzle with remaining 2 tablespoons oil. Serve immediately.