1 ¼ - 1 ½ lb. rapini (broccoli rabe), ends trimmed
3 tbsp. EVOO
½ small red onion or 1 large shallot, finely chopped
1 lb. bucatini
4 oz. 'nduja
4 cloves garlic, sliced or chopped
1 lemon, zested and halved
1 cup grated pecorino
Prepare a bowl of ice water. Bring a large pot of water to a boil, salt it, and cook the rapini for 3 minutes. Drain rapini and place in bowl with ice water. Refill the pot with water and return to a boil (for the pasta). Once the rapini has cooled, transfer to paper towels to drain, then chop into bite-size pieces.
In a large skillet, heat the EVOO, three turns of the pan, over medium-high. Add the onion and season with salt. Cook for 3 minutes, then add about 1/2 cup of water. Simmer until the liquid evaporates.
Salt the water once it's boiling, then add the pasta. Cook 1 minute less than the package directions. Reserve about 3/4 cup of pasta cooking water before draining.
Add 'nduja to pan with onion and cook, breaking up with a wooden spoon, until 'nduja darkens in color, about 3 minutes. Stir in the garlic for a minute or two, then add rapini and lemon zest to heat through. Add the pasta, reserved pasta water, half the pecorino, and juice of half the lemon. Toss for 1 minute and top with remaining pecorino.