Prepare the sauce first. Heat a medium saute pan over medium-high heat. Add the 3 tablespoons olive oil, then the onions. Sauté until onions are softened, about 5 minutes. Add the garlic and sauté another minute. Add the tomatoes, basil and 2 Tbsp oregano, salt and pepper. Reduce heat to medium-low and cook until slightly reduced, about 20-30 minutes.