Heat the oven to 200C/180C fan/gas 6. For the base, put the flour in a large bowl. Whisk in 250ml water to make a batter. Heat the oil in a large, non-stick frying pan. Pour in the batter and cook over a low heat for 4-5 mins until set. Loosen with a palate knife or spatula, turn and cook for 1-2 mins on the other side.
Meanwhile, for the toppings, heat the oil in a pan over a medium heat and stir-fry the mushrooms and peppers until soft, about 4-5 mins. Mix the tomato purée and garlic in a bowl with 2 tbsp water, then stir in the chopped tomatoes.
Turn the base out onto a baking tray lined with baking parchment. Spread over the tomato mixture. Scatter over the mushrooms, peppers, half the basil and the cheese. Bake for 5-10 mins until the cheese has melted. Scatter with the remaining basil to serve.
