Stir the potatoes, thyme, black pepper and oil in a 13x9x2(3 qrt) shallow baking dish in a single layer.
Bake at 400 degrees F for 20 mins. Stir. Bake for 15 mins. more or until the potatoes are fork tender and golden brown.
Reduce the temperature to 350 degrees F. Stir the soup and water in a small bowl. Pour soup mixture over the potatoes. Sprinkle with the onions. Bake for 15 mins. more or until hot and bubbly. Serve immediately.