Couscous: Bring 2 cups/500 mL water and salt to boil; add carrot and boil until tender-crisp. Add zucchini and celery; boil for 1 minute. Stir in couscous; return to boil. Cover and remove from heat; let stand for 15 minutes. Fluff with fork. Keep warm.

Meanwhile, clean mussels under cold running water, discarding any that do not close when tapped. Pull off any beards.

In large saucepan or Dutch oven, heat oil over medium heat; add fennel seeds and hot pepper and fry until fragrant, 20 to 30 seconds. Add onion and garlic; fry until onion is softened, about 3 minutes. Stir in all but 1 tbsp/15 mL of the parsley and the salt; fry for 30 seconds.

Add tomatoes and orange rind and juice, breaking up tomatoes with spoon; increase heat to medium-high and bring to boil. Stir in mussels. Cover and cook until mussels open, about 7 minutes.

Transfer couscous to serving platter or individual plates. With slotted spoon, transfer mussels, discarding any unopened ones, and arrange over couscous.

Boil sauce, uncovered, until slightly thickened; remove from heat. Stir in remaining parsley. Spoon over mussels.