Preheat the oven to 230°C (gas mark 8), placing a pizza stone inside if you have one.
Lightly dust a pizza peel or a large baking tray with plain flour.
Gently stretch or roll out the pizza dough into a 30cm circle.
In a small bowl, mix the tinned chopped tomatoes with the dried oregano, garlic powder, salt and a pinch of black pepper.
Transfer the dough to the prepared peel or baking tray, drizzle with olive oil, then spread the sauce evenly, leaving a 1cm border.
Scatter the fresh mozzarella over the sauce.
Top with the sliced pepper, mushrooms and thinly sliced red onion.
Slide the pizza onto the hot stone or place the baking tray on the middle shelf and bake for 12–18 minutes, until the crust is golden and the cheese is bubbling.
Remove the pizza from the oven and let it rest for a few minutes. Scatter the torn basil leaves over the top, then slice and serve with a green salad.