Preheat oven to 200°C (180°C fan-forced). Lightly spray the base and sides of a 7cm x 11cm x 21cm (base) loaf pan with cooking spray.
Place the couscous in a large heatproof bowl, pour over boiling water. Cover and stand for 5 minutes then stir the couscous gently with a fork to separate the grains. Set aside to cool.
Place the chopped onion on a microwave safe plate, spray lightly with oil and cover with damp paper towel. Microwave for 2 minutes on high/100%. Set aside to cool.
Combine the mince, grated vegetables, tomatoes, egg, parsley, onion and couscous together in a large bowl. Season well with pepper and mix well using clean hands. Press mixture into loaf pan. Bake for 40-50 minutes or until firm in the centre. Stand in the pan for 10 minutes before turning onto a board.
Slice with a serrated knife and serve with salad.