1. In a large mixing bowl, combine flour, yeast, sugar, and salt. Add warm water and vegetable oil. Mix until a dough forms.
2. Knead the dough on a floured surface for about 10 minutes, until smooth and elastic.
3. Place the dough in a lightly oiled bowl, cover with a damp cloth, and let rise in a warm place for about 1 hour, or until doubled in size.
4. Preheat the oven to 475°F (245°C). Line a baking sheet with parchment paper.
5. Punch down the dough and divide it into 8 equal pieces. Shape each piece into a ball and place on the prepared baking sheet.
6. Flatten each ball slightly and make a small indentation in the center. Fill each indentation with the onion and poppy seed mixture.
7. Bake in the preheated oven for 12-15 minutes, or until golden brown.
8. Let cool on a wire rack before serving.