Put the flour, yeast, salt and oil in a large bowl then stir in the water with a wooden spoon a little at a time until the dough is very soft and wet. You may not need all the water.
Turn out on to a floured work surface and knead (with oiled hands to prevent the dough sticking) for about five minutes. Place in a large oiled bowl, cover with clingfilm or a clean tea towel and leave to rise in a warm draught-free place for one hour.
Preheat the oven to 220°C/430°F/Gas Mark 7.
Lightly oil a baking tray. Tip the dough out on to the tray and spread the dough to the edges of the tray using the tips of your fingers, ensuring it is spread evenly. Leave to rise, uncovered for about 20-30 minutes.
Gently prod the dough with your fingers to make slight impressions on it, then scatter over the onions, tomatoes, spinach and pine nuts. Sprinkle over sea salt. Bake in the oven for 20-25 minutes until golden and risen.