Place flour, sugar, oil, water, baking powder, vanilla, and salt in a standing mixer fitted with a flat beater. Mix just until a uniform dough is obtained. If the dough is not coming together, add a little water (1-2 teaspoons).
Shape the dough into a disk about 1 inch thick before chilling. Wrap the dough in plastic wrap and transfer it to the refrigerator for 1 to 2 hours (up to overnight). Roll the dough on a heavily floured surface to a ¼ -inch (½ cm) thickness and cut circles using a cookie cutter. Place a flat teaspoon of the filling of your choice in the center of each circle. *The dough is going to be sticky so flour the dough and rolling pin as needed* Pinch the edges together in three places so that they meet in the middle to form a triangular cookie shape. Pinch the three corners of the triangle together firmly to seal the edges. Make sure the filling is well-enclosed.
Arrange the Hamantaschen on a baking sheet lined with parchment paper. Place the baking sheet in the freezer for 30 minutes to an hour before baking.
Preheat the oven to 350°F/180°C.
Pinch the hamantachen's corners again to ensure they won't open in the oven.
Bake for 15-20 minutes until the Hamantaschen is slightly golden. Let them cool.
Dust with powdered sugar.