Heat olive oil, add vegetables and salt and cook on medium/low until brown, about 30 minutes. Spread three-cheese salad dressing on top of the naan bread. Top with grated Parmesan cheese. Spread vegetables on top and cover with a mixture of grated cheddar & mozzarella. Heat oven to 400°F (205° C) and place directly rack in middle of oven. Bake 8-10 minutes until cheese is browned and bubbling.