In a large bowl, add flour, salt, sugar, and instant active dry yeast.
Slowly, pour in warm water and stir with a wooden spoon or dough whisk.
Next slowly add 1/4 cup of olive oil and continue to stir. The dough will be sticky, but it will not be watery. If it appears watery, add more flour.
Cover the bowl with a clean tea towel or plastic wrap and let the dough rise for a minimum of two hours at room temperature.Take note the dough will do best in a warm environment. If it is not a warm environment, place it in your oven with the oven light on.
Using a 13 inch baking dish or focaccia baking pan, coat thepan with olive oil.*Note - alternatively you can use a large baking sheet, the focaccia will not be as tall but still amazing! After the focaccia dough has risen, place the dough gently into the greased baking dish. Coat your hands with olive oil, so they will not stick to the dough and push the dough gently until it fills the entire baking dish evenly.
When finished, let the dough rise for another 30minutes.
Preheat your oven to 400°F
After the focaccia dough has risen a second time in the baking pan, press your fingers over the dough to make indentations.
First gently press olives into dough, next, lightly spread the dough with crushed San Marzano tomatoes, next place thinly sliced red onion on top. Sprinkle the top with dried oregano, salt and pepper.
Bake in the lower section of your oven for 20 to25 minutes.
This last step is optional… I like to turn my boiler on andplace the pan on the top shelf of my oven and broil it for one minute, to get the crust very golden brown. *Note… I have tried to make this recipe several different ways, and I highly recommend letting the yeast rise for two hours or more for the first rise, and30 minutes or more for the second rise. It will give you the most beautiful focaccia you have ever seen.