Step 1Heat the oven to 350 degrees. Spread the pine nuts on a baking sheet and toast in the oven until golden, about 10 minutes. Set aside.
Step 2Bring a big pot of salted water to a boil over high heat. While it is heating, prepare the squid. Cut the section of tentacles in half lengthwise so that you have two bunches of tentacles still attached at the base. Slice each tube along one side lengthwise, so that you can open it out flat. When you spread the tube open, it will look like a triangle. Cut each triangle in half lengthwise, and then crosswise in roughly 2-inch sections. Using a very sharp knife, lightly score the surface of each section in a crosshatch pattern, cutting into but not through the flesh. Alternatively, simply cut the tubes in half-inch rings.
Step 3In a large mixing bowl, whisk together the olive oil, lemon juice, garlic, fennel fronds and salt.
Step 4Blanch the squid in the boiling water, about a quarter at a time. Cook until the squid curls up, firms and becomes opaque, about 20 to 30 seconds. Remove with a slotted spoon or wire skimmer and immediately place in the dressing. Repeat until all squid has been cooked and is in dressing.
Step 5Cut each fennel bulb in quarters lengthwise and trim out the solid core in the center. Slice crosswise as thinly as possible and add the fennel to the dressing. (The recipe can be prepared to this point several hours in advance and refrigerated tightly covered.)
Step 6When ready to serve, add the arugula to the squid and fennel and toss to combine. Divide evenly among 4 to 6 chilled plates and scatter pine nuts over the top. Serve immediately.