Wash the rosemary, shake dry and pick off the leaves. Finely chop the leaves and mix with 2 tbsp olive oil.
Brush the mushrooms and cut into pieces.
Peel and finely dice the onions and garlic.
Heat the remaining oil in a pan and fry the onions and garlic over a medium heat for 1 minute. Add the mushrooms and fry for 3-4 minutes, stirring. Season with salt and pepper.
Coarsely grate the goat's cheese.
Divide the pizza dough into 4 pieces and roll out to about 0.5 inch thick ovals. Place 2 flatbreads on each floured baking tray.
Brush the flatbreads with the rosemary oil then add 2 tbsp tomato sauce.
Scatter the mushrooms over the flatbreads and sprinkle over the cheese. Bake in the preheated oven at 445°F (425°F fan, gas 8) for 12-15 minutes.