Greek Vegetable Medley (vegan)

2 tablespoons olive oil -- divided
3 medium onions -- sliced
2 cloves garlic -- minced
2 pounds medium potatoes, peeled & sliced -- into 1/4" rounds
2 pounds large zucchini, sliced -- into 1/3" rounds
1 large red bell pepper, seeded & -- cut into thin rounds
1 large green bell pepper, seeded & -- cut into thin rounds
salt & freshly ground pepper to taste
1 1/2 cups plum tomatoes, coarsely chopped -- drained of juices
1/2 cup chopped parsley
1 teaspoon dried oregano
water

1. Heat oven to 170 degrees C.
2. Heat 1 tablespoon of oil in a large nonstick skillet and cook onions and garlic until onions are softened or about 5 minutes.
3. In a large shallow baking dish coated with cooking spray, place potatoes, zucchini, and peppers in one overlapping layer, alternating them.
4. Season with salt and pepper and sprinkle with sauteed onions and garlic.Pour tomatoes evenly over layered vegetables, season with parsley and oregano, and add remaining 1 tablespoon of olive oil. Add enough water to come halfway up the vegetables.
5. Bake for 1 to 1 1/2 hours or until all the vegetables are tender.