Cut the roots off the radicchio grumolo and separate the leaves, then rinse them. Set aside.
Flake the haddock with 2 forks into bitesized pieces and set aside. It should be easy enough to do.
About 3 minutes from the end of the spaghetti cooking time, heat the olive oil on medium high heat, in a large frying pan.
Add the haddock and cook for about 1 minute, stirring constantly.
Add the garlic, fry for 20 seconds.
Drain the spaghetti and add to the frying pan.
Save one handful of the radicchio grumolo and add the rest to the pan with the spaghetti.
Stir vigorously and mix thoroughly for 1 minute.
Take off the heat, add the pepper flakes and freshly ground black pepper. You shouldn't need any salt as the haddock would have been salty enough.
Serve the pasta onto 2 plates, squeeze the lemon juice all over both plates of pasta, followed by the parsley and the reserved radicchio and serve immediately.