Prepare the dough: Place the flour, yeast, sugar, oil, water, and salt in the bowl of a stand mixer fitted with the dough hook attachment. Mix until a smooth and elastic dough forms, about 10 minutes. Cover and let the dough rise for 1 hour.
Prepare the filling: Heat the oil in a shallow pan over medium heat. Add the onions and sauté until soft and golden, 5 mi