To make the topping place a frying pan over a lit hob and pour in a splash of oil.When fully heated add the onions and fry them until soft. Add the peppers, mushrooms, garlic, onion and the chili. Leave to fry for another 1-2 minutes. Add the chopped tomatoes, tomato puree, fresh basil, oregano and season to taste. Mix well and add spoonfuls of the topping onto the pizza base leaving roughly 1 inch around the edge. Make sure the topping is evenly spread. Evenly sprinkle the mozzarella over the pizza and place in the oven for 10-15 minutes or until crisp and golden.