Preheat the oven to 220°C.
Peel the potatoes and cut them into medium to small size pieces.
Put them in a large bowl, add the tomato sauce, and stir until marinated.
Transfer to a baking sheet, add 1 cup water, and place in the oven for about 45 minutes until cooked through. Baking time depends on the size of the potatoes and the oven, so be careful and continue to check them after the first 30 minutes!