Heat oven to 350 degrees. Heat 1 tbsp oil in large nonstick skillet over medium heat and cook onions and garlic until softened or about 5 minutes In a large shallow baking dish coated with cooking spray, place potatoes, zucchini and peppers in one overlapping layer, alternating them. Season with salt and pepper and sprinkle with sauteed onions and garlic.
Pour tomatoes over layer veggies, season with parsley and oregano and add remaining 1 tbsp olive oil. Add enough water to come halfway up the veggies. Bake 1 to 1 1/2 hours or until all veggies are tender.