Mix together the yeast with the warm water and let sit until bubbly. Place the flour in a large bowl, and add the olive oil, salt, yeast mixture and oregano. Mix well with a spoon, then remove the dough to a hard surface and knead for about 8 minutes or until the dough is smooth. Place the dough in a lightly oiled bowl and cover to let rise 1 hour or until the dough doubles in size.
Heat the oil and butter until sizzling. Add the onions and stir well to coat with the oil mixture. Cook over low heat until the onions are very soft and golden brown, about 45 minutes or so. Stir the fresh rosemary into the onion mixture.
Preheat the oven to 450 Degrees F. Punch down the dough and place onto an oiled baking sheet. Shape into either a circle or rectangle about 14 inches across. Spread the onion mixture evenly across the dough and then add the olives and capers. Sprinkle on some sea salt and cracked black pepper and then drizzle with a little additional olive oil. Bake about 20 minutes, or until golden brown and crisp. Cut into slices and serve warm.