Cook the pasta according to the packet's instructions (usually boil for 10 minutes.)
Steam the broccoli florrets over the pasta water for 5-8 minutes until bright green and tender. Place to one side to cool while the pasta finishes cooking.
Remove the pasta from the heat once cooked, drain, then run under cold water until pasta is completely cool.
Transfer the pasta and cooled broccoli to a bowl and add the mayonnaise, lemon juice, and raisins.
Stir thoroughly until all of the ingredients are combined and coated in the mayonnaise.
Season to taste before topping the dish with the walnuts and grated parmesan.