Place the cubed potatoes, water, lemon juice, vegetable oil, and olive oil in a 12x18 inch baking dish or roasting pan. Season with oregano, salt, pepper, and garlic.
Roast, uncovered, in the preheated oven until the potatoes are tender and golden brown and the water has evaporated, about 1 1/2 hours. Stir the potatoes every 20 minutes as they bake, adding more water as necessary to prevent sticking. Allow the water to evaporate during the final 15 to 20 minutes of cooking, but be careful that the potatoes do not burn. Stir in the chopped fresh parsley, and serve.
