Special equipment: bamboo skewers, soaked for 30 minutes or metal skewers
For the vinaigrette: Add the grapefruit juice and vinegar to a medium bowl. Add the olive oil while whisking to combine. Season with a pinch of salt and pepper.
For the calamari salad: Mix together the oil, chili flakes, garlic, lemon juice and zest, parsley and some salt in a large bowl. Add the calamari, toss together and let marinate for 20 minutes or up to 1 hour. Preheat a grill to high heat. Remove the calamari from the marinade and skewer them. Skewering the rings of the calamari onto 2 skewers each will help to keep them on the skewer and not fall off into the grill. Sprinkle with salt and pepper, and grill for about 2 minutes per side. They should be slightly charred and opaque. Add the calamari, arugula, grapefruit segments, fennel and vinaigrette to a large bowl and toss. Season with salt and pepper and serve immediately.
I don't use the tentacles of the calamari in this recipe, but you can use them. Just be careful they don't fall off the skewer into the grill. This recipe can also be made indoors, cooking the calamari in a skillet.