Preheat the oven to 190°C (170°C fan). Grease a 23cm springform tin with olive oil.
Press one pizza base into the bottom and up the sides of the tin.
Spread one-third of the marinara sauce over the base, then scatter one-third of the shredded mozzarella.
Top with half the sliced pepperoni, half the diced green pepper and half the diced red onion.
Place a second base on top and repeat with another third of the sauce, cheese, pepperoni, pepper and onion.
Finally, top with the last base. Spread the remaining sauce over the top and sprinkle on the remaining cheese.
Bake for 30–35 minutes, or until the crust is golden and the cheese is bubbling. Cover loosely with foil if the top browns too quickly.
Leave to cool in the tin for 10–15 minutes before releasing the sides. Slice and serve warm.