In a mixing bowl, combine sourdough discard, all-purpose flour, baking powder, olive oil, and a pinch of salt. Stir until a shaggy dough forms.

Cover the dough with a clean kitchen towel and let it rest for about 10 minutes.

Divide the dough into 12 equal pieces and roll each into a ball. Flatten each into a 3-inch round circle.

Take one round of dough, place a cube of mozzarella in the center, and add your choice of filling. Pinch the edges to seal.

Place the sealed pizza bombs on the prepared baking tray, sealed-side down. Preheat the oven to 375°F and bake for 18-20 minutes.

Remove from the oven, let cool for a few minutes, and serve warm with marinara sauce.