- Preheat the oven to 200°C, fan 180°C, gas mark 6, and line 2 baking trays with baking paper.
- Put the yogurt and the flour into a mixing bowl and season well. Mix until a soft dough forms.
- Dust a work surface with the flour. Divide the pizza dough into 4 pieces and roll out each piece to a 15cm circle. Transfer to the prepared baking trays, scatter over the onion then top with the tomato slices.
- In a small jug, combine the harissa paste, vinegar and oil, then season well. Drizzle or brush the harissa mixture over the tomato slices, then bake the tarts for 20 minutes until the dough is crisp and golden.
- Spoon over the yogurt, scatter over the chopped parsley and serve with the rocket on the side.