Preheat the oven to gas 6, 200°C, fan 180°C and grease a baking tin with oil.
Arrange the sweet potato in the prepared tin and roast in the oven for 40 minutes, until tender. Place the pine nuts in a second tin and put in the oven for the last 10 minutes of the potato cooking time. Shake the tray after 5 minutes, so the pine nuts brown evenly. Take care not to let them burn.
Spread the pizza sauce on each pizza base and top with slices of onion. Divide the sweet potato between the pizzas and put the pizzas in the oven for about 10 minutes or until the bases are cooked.
Place the pizzas on warmed plates and top each one with spinach leaves, feta cheese and a sprinkling of pine nuts. Drizzle with a little olive oil and balsamice vinegar and serve at once.
This is a great recipe for vegetarians and using ready-made pizza bases and a jar of sauce makes it a speedy healthy supper dish for a family of four.
*Inspired by Erin H. featured in the Realfood Cookbook