Bring a large saucepan of water to a boil over high. Add broccoli rabe; boil until crisp-tender, about 2 minutes. Using tongs or a slotted spoon, transfer broccoli rabe to a colander. Rinse under cold water (or dunk in a bowl of ice water) to cool to room temperature; squeeze gently to remove excess water. Set aside. Return water in pan to a boil over high. Add pasta; cook until al dente, about 12 minutes. Reserve 2/3 cup cooking liquid. Drain pasta; set aside. Heat oil in a large skillet over medium-low. Add garlic, red pepper, and 1/8 teaspoon salt; cook, stirring often, until garlic is tender, about 5 minutes. Add cheese and reserved 2/3 cup cooking liquid; stir until cheese melts. Stir in broccoli rabe and pasta; cook until warmed, about 2 minutes. Sprinkle with zest and remaining 3/4 teaspoon salt. Toss well to combine.