In a large bowl, mix 360ml lukewarm water with a 7g sachet of dried yeast and 1 teaspoon of caster sugar. Stir gently and leave to stand for 5 to 10 minutes, or until foaming.
Add 420g plain flour, 2 teaspoons of salt and 2 tablespoons of olive oil to the yeast mixture. Stir until a rough dough forms.
Tip the dough onto a lightly floured surface and knead for 5 to 7 minutes, or until smooth and elastic, adding a little more flour if it's too sticky.
Lightly oil a clean bowl, place the dough inside and turn to coat. Cover and leave in a warm place for 1 to 1.5 hours, or until doubled in size.
While the dough is rising, make the sauce. In a small bowl, mix a 400g tin of chopped tomatoes with 2 crushed garlic cloves, 1 teaspoon of dried oregano, 1/2 teaspoon of dried basil, 1/4 teaspoon of salt and a pinch of freshly ground black pepper. Stir and set aside.
Prepare the toppings: grate 225g low-moisture mozzarella, slice 80g pepperoni and 100g mushrooms, and thinly slice 1/2 green pepper and 1/4 small red onion.
Preheat the oven to 250°C (gas mark 9) or 230°C for a fan oven. Place a pizza stone or heavy baking tray in the oven to heat.
Knock back the dough, divide it in two, and stretch one portion into a rough 30cm round on a lightly floured surface or sheet of baking paper. Transfer to the preheated stone or tray.
Spread half the sauce over the base, leaving a 1cm border. Sprinkle half the cheese, then arrange half the pepperoni, mushrooms, green pepper and red onion. Brush the edge with a little olive oil, if you like.
Bake for 12 to 15 minutes, or until the crust is golden and the cheese is melted and bubbling with a few brown spots.
Transfer the pizza to a wire rack and leave for a couple of minutes before slicing. Repeat with the remaining dough and toppings, then serve straight away.