Heat oven to 220C/200C fan/gas 7. Tip the flour into a mixer with a dough hook, or a bowl. Add the yeast, salt, oil and just under 100ml warm water then mix to a soft dough. Knead in the food mixer for about 5 mins, but if making this by hand, tip onto a work surface and knead for about 10 mins. The dough is sticky, but try not to add too much extra flour. Leave in the bowl and cover with a tea towel while you make the topping. There is no need to let the dough prove for a specific time – just let it sit while you get on with the next step.
Tip the onions into a non-stick wok and add the oil, 4 tbsp water and balsamic vinegar. Cover with a saucepan lid that sits inside the pan to help the onions soften, then cook for 15 mins, stirring about 3 times and replacing the lid quickly so as not to lose too much moisture. After the time is up, the onions should be golden and all the liquid gone. Tip onto a plate. Add the spinach and garlic to the pan and stir-fry until the spinach has wilted.
Take the dough from the bowl and cut in half with an oiled knife, then press each piece into a 25-15 cm oval on a large greased baking sheet with oiled hands. Don’t knead the dough first otherwise it will be too elastic and it will keep shrinking back.
Spread with the spinach followed by the onions, then dot with the cheese and scatter with the olives, thyme and sunflower seeds. Bake for 15 mins until golden and the base is cooked through.