Preheat the oven to 160˚C /325˚F.

In a large bowl, dissolve the yeast in the warm water and cover with a kitchen towel. Let stand for 5 minutes or until it starts to bubble. Combine the two flours and salt. Slowly add the flour to the yeast mixture, mixing with a wooden spoon until a dough mass forms. Add a little more water as needed if the mixture is too dense, or, add a little more flour if it is too loose. Knead in the bowl until smooth and pliant and the sides of the bowl come clean. This can also be done in a mixer with a dough hook on medium speed. Cover the bowl with plastic wrap and set aside for 1 hour to rise.

Meanwhile, heat the olive oil in a large skillet over medium heat and cook the onions for about 5 minutes or until they start to soften. Add the chopped tomatoes, raise the heat to medium-high and cook until most of the liquid has cooked off. Remove from the heat.

Oil a large, preferably square or rectangular baking pan. Roll out the dough on a lightly floured surface to the size of the plan and place inside. Cover and let the dough rise for 15 minutes.

Spread the tomato-onion mixture evenly over the dough. Season with salt, pepper and oregano and bake for about 1 hour or until the dough is crisp and the topping is caramelized. Remove, cool slightly and serve.