Step 1: Preparing the Dough

1. Combine flour, yeast, sugar, and salt in a bowl.
2. Add lukewarm water and oil, mixing until a dough forms.
3. Knead for 10 minutes until smooth and elastic.

Step 2: Proofing the Dough

1. Place the dough in a greased bowl, cover with a damp cloth, and let it rise in a warm spot for about 1 hour until doubled in size.

Step 3: Caramelizing the Onions

1. While the dough is rising, heat oil in a skillet over medium heat.
2. Add the chopped onions and cook slowly, stirring occasionally, for 15-20 minutes until they turn golden brown.
3. Season with salt and pepper to taste.

Step 4: Shaping the Flatbreads

1. Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
2. Punch down the dough and divide it into 8 equal pieces.
3. Roll each piece into a ball, then flatten into a disk about ¼-inch thick.

Step 5: Adding the Toppings & Baking

1. Arrange the dough disks on the baking sheet.
2. Spread the caramelized onions evenly on each disk and sprinkle with poppy seeds.
3. Bake for 15-20 minutes until the edges turn golden brown.

Step 6: Serve and Enjoy

1. Allow the cebularz to cool slightly before serving.
2. Enjoy warm or at room temperature with your favorite soup or as a standalone snack.