Preheat oven to 400°F (200°C). Line a baking sheet with parchment.

Steam riced cauliflower until tender, about 8 minutes. Drain and press firmly in a clean towel to remove excess moisture.

Mix cauliflower, mozzarella, egg, and almond flour into a dough.

Heat olive oil in a skillet over medium heat. Add onion and cook 5–6 minutes until softened. Stir in corned beef and mustard powder, cooking 2–3 minutes to combine.

Divide dough into 8 pieces and flatten each into a small round. Spoon filling into the center and fold the dough up around it, pinching to seal.

Arrange seam-side down on the baking sheet, brush with beaten egg, and bake 20–22 minutes, until golden.