How to Make It
In a medium bowl, mix the marjoram, ground fennel and orange zest with 1/2 cup of the olive oil, 1/4 cup of the chives, 2 tablespoons of the parsley and half of the minced shallots. Season the marinade with salt and pepper and pour into a shallow baking dish. Add the mackerel, turn to coat and refrigerate for 1 hour.
Meanwhile, fit a food processor with a coarse shredding disk. With the machine on, drop the cauliflower florets through the feed tube without pressing and process until finely grated. Transfer the cauliflower to a medium bowl and toss with 1 tablespoon of salt. Let stand at room temperature for 30 minutes.
Drain the cauliflower and squeeze out any liquid; return the cauliflower to the bowl.
In a small skillet, heat the remaining 6 tablespoons of olive oil. Add the minced garlic, cumin and paprika and the remaining minced shallot and cook until the mixture is fragrant, about 2 minutes. Let cool slightly, then pour the mixture over the cauliflower. Add the preserved lemon rind, mint, tomato, sherry vinegar and the remaining 1/4 cup each of parsley and chives to the cauliflower. Season the tabbouleh with salt and pepper and toss.
Light a grill. Grill the fish fillets over moderately high heat, turning once or twice, until they are nicely charred in spots, about 7 minutes. Serve the fish with the cauliflower tabbouleh.