In a large resealable plastic freezer bag, mix the olive oil, parsley, oregano, basil, vinegar, salt, pepper and garlic.
2.
Place the onion, asparagus, mushrooms, eggplant and capsicums into the bag. Seal, shake gently to distribute the marinade and set aside at least 2 hours in the refrigerator.
3.
Preheat the barbecue for high heat.
4.
Lightly oil cooking flat plate. Cook the vegetables 6 minutes on each side or until tender.