Preheat a barbecue to medium heat. Cut two sheets of heavy duty aluminum foil each approximately 45cm long.
Place the yellow zuchinni, green zucchini, tomatoes, onion and garlic in the centre of one sheet of foil. Drizzle with olive oil then season with salt and pepper. Place second sheet of foil on top of vegetables. Fold edges together tightly to seal packet.
Place packet on the top rack of the preheated barbecue. Cook for 15 minutes. Turn packet over and continue to cook until vegetables are tender; 15 to 20 minutes.
Carefully cut an "X" into top of foil packet and pour vegetables and juices into serving bowl. Garnish with parsley.
For a spicier option add 2 tablespoons of red wine vinegar, 1 tablespoon of oregano, and 1 tablespoon of hot sauce. This adds a slightly different colour along with a robust flavour to the zucchini.