Bring a large pot of water to a boil. Add enough salt so that it tastes like the saltwater of the sea.
In a bowl, whisk the olive oil, lemon zest and juice, and red pepper flakes or Fresno chile together until combined.
Drop the rapini into the boiling water and blanch for 30 seconds. Drain, shaking the colander forcefully to remove as much water as possible, and transfer to the bowl with the dressing.
Toss well, transfer to a serving dish, and sprinkle with the Maldon salt and a few cranks of black pepper.